Not engaging with his ex for any reason is perfectly fine and actually a good boundary to maintain if it brings you a level of peace.  Relationships are fluid and any man that tells you “kids will always come first” has zero clue of how to be in an effective relationship.  Reality is who comes first will always be shifting and moving.  The fact that he moved away from his kids to be with you was a choice he made and not one for you to feel guilty about.  Having minimal participation in his children lives is your choice and one you should not feel guilty about if it’s what makes you happy.  Don’t feel like you have to buy into the bullshit social norms of being their mom or loving them like your own, because you don’t have to and they aren’t your children.  As long as you and your DH are communicating your wants and needs and working with one another on any issues I don’t see why either of you should feel guilty about anything.

I refused to deal w/ his ex. I don't poke her with my junk so she wasn't in my circle of people to deal with. I also didn't participate w/ his son in the begining. I tried to respect their relationship. But in all honesty, with a few hiccups, we all found what worked for us. Yes there were times when it seemed unfair or wrong but we kept our line of communication open and worked through it all. 

His minor children are his primary OBLIGATION.. they are reliant on him for support.. food.. housing.. ie parenting.

However, children are not the only and constant PRIORITY.  There will be times that he will have needs for resources.. time.. money.. that his kids don't.. same for you.. Your need for him to go to your parent's funeral trumps him going to his kid's little league game.  Taking care of a sick kid during his visitation may trump those dinner plans you thought you had.  That's how families work.. not everyone is first in line.. there are limited resources.. time.. money.. and not everyone will get first in line.

His kids don't get to sit in the front seat.. his kids don't dictate every restaurant.. movie.. color of your walls.. there are adult decisions that kids need to be taught to accept right?

Will your life be different and will there be some constraints due to him having kids.. yes.. of course.. he has a portion of his paycheck pre spent.. he doesn't have full autonomy over that.. there will be times that you want to go do something and he will have a prior comittment with his kids.. again.. how families work.. 

Your wishes and needs don't always come in last.. but ALSO.. you are an adult.. you can pay for your own desires.. and you can go do your own thing while he does his kid's thing too.. that is an option.

As far as Co-Parenting.  To me what that really should mean is that the parents have a generally similar approach to parenting the kids.. but not that they confer and discuss every detail.. He parents on his time.. She parents on her time.. NEITHER of them attempt to overrule or PAS the kid against the other parent.. and when they may have their kid come to them and complain about the other household rule?  the correct response is almost always.

"Well, that is your mom's rule and her house.. so she has the right to that rule and you need to follow it when you live there"  

You don't undermine the other parent.. even when you might have different rules.  Like you allow eating in the family room.. the other house does not.. that's the rule.. not your call to make.

coparenting can include agreement on things that will impact both homes.. like kid activities.. and may include coordination of bigger things like driving or going to college.  A serious behavioral issue may also be discussed.. but day to day petty? no.. each side figures it out.. though letting the other person know is good.

aka.. "We have had issues with Timmy taking things that don't belong to him at home and at his friend's homes.. please watch out for that and reinforce that we don't touch other people's belongings without permission"

Co-parenting means Mom and Dad agree to the same rules in each household. It means negotiating if you don't agree. Communication varies - usually dependent upon the age of the child & their behavior. It is easier for the child because they have the same expectations in each household. You need two stable parents to do this. 

Parallel parenting means my house; my rules. This is what we most follow here. High conflict parents make co-parenting unattainable as they have a my way or the highway attitude. 

Either style of parenting shouldn't really have anything to do with a step-parent other then deciding on the rules in a joint household. 

A lot of good advice here. And I agree on the communication. If you don't want to deal with BM, don't. Set that boundary. Really, it's your DH's role. Not to mention, there can sometimes be complicated feelings when exes are involved. There's often less opportunity for drama if the stepparent stays out. Since day one, DH has handled all contact with BM with one exception -- one time in an emergency where DH's phone was out of commission. BM and I get along fine -- in part because our only communication is a friendly "hi" at events.

Also, she likes me. Why? Because I don't overstep. My whole plan from the start was to stay in my lane. I'm there to help DH. I will advise if asked. But I do not steer the ship. Big decisions are for them to make. I have a say in DH's say, but no vote of my own.

DH and BM split custody 50/50 and they work well together in some ways. They communicate nicely and are cooperative with schedule changes. Some problems are getting bigger regarding the different parenting styles (she spoils SS rotten and is very permissive, while DH has rules and expectations) but, for now, it's manageable.

My hands-off approach did not go over too well in the beginning. Like many bioparents, DH had visions of the three of us as a happy family. It took years, but he finally realizes that his perfect family wasn't going to happen because it wasn't realistic.

As for societal pressures -- hoo boy. I used to feel guilt about that because I felt no connection with my SS. Even though I adore my sisters' kids, the love just wasn't there. Reading a book called Stepmonster actually helped a lot, as it spelled out how expecting women to love stepchildren like their own is not only unrealistic, it's unnatural. If it happens, great. If not, there's nothing wrong with that. It's a complicated relationship that few outsiders can understand. And, in my case, I have a SS who, while not a bad kid, is just not easy to get attached to.

I believe it's important for kids to have individual time with their dad. Sometimes I go along on trips or outings with DH and SS, sometimes not. Little League games and practices? I'm there. Saturday morning bowling league? That my "me time."

Effective co-parenting is not possible when you have a controlling parent on one side and an irresponsible, self-serving parent on the other. 

Your BM sounds controlling...but part of this seems to be as a direct response to your DH being flakey, self-serving and high-conflict. 

Your DH woke up one fine day, and decided he doesn't want to have his kids overnight or be really involved in his kids' lives. This affects both BM and his kids negatively because a) this puts more burden on BM (who didn't make these kids on her own, so they shouldn't be only her responsibility, should they? b) the kids are at a higher risk of abandonment issues and psychological issues that stem from their not having an involved father ( issues that BM will also have to deal with);

Your DH thinks he's entitled to make these decisions, that negatively affect other people, uunilaterally, whilst expecting these same people to just accommodate him. He decided to barely see his kids, he doesn't even have space for them, thus completely relying on BM and "her support system" to raise his kids, drive his kids to places, emotionally support his kids , house his kids etc.. At the same time (to add insult to the injury) he spends the little time he has with his kids undermining BM's parenting and going against her, for seemingly no reason at all, other than to be spiteful.

I can see why BM would be a bit salty about all of this. Because not only is your DH  uninvolved in the kids lives, he uses the little time he has to create even more problems. He's not making these "parenting" decisions in his kids' best interest for sure. His kids don't need to eat beef and they don't need a phone at 10 and 6 years old. So why is he making these decisions, other than out of spite and to serve his own interest? If he has decided to be merely the hands-off "fun" uncle in his kids' lives,  then the least he could do, is respect the choices of the person who is actually raising his kids all on her own, and stop creating drama for no reason. 

You don't want to hear the advice 

You and your DH do not have a leg to stand on here. You're simply not in the right. 

It was not BM who cut your DH out of his kids's lives. It was your DH who did that, and you encouraged him to do that. It's simply not your place to decide custody arrangements and what's best for these kids. Ironically, you complain about BM being controlling but your trying to control when and how your DH sees his kids, is very controlling. BM is concerned about the effect this will have on the kids, and rightly so! She will be the one mostly picking up the pieces, after all!

 Your DH didn't want to have his kids overnight anymore, and you don't want him to either because you're not comfortable with kids running around. Well, you did marry a man with kids!

I don't know what you expect here. You want to hear that you and your DH are in the right, and that the kids will just turn out fine. That's not reality. The reality is your DH is being very irresponsible and self-centred as a father,  and you tryng to dictate to him when and how he sees his kids and what's best for his kids, is overstepping and controlling. Disengage and do not stand in the way of your DH being a responsible father and spending time with his kids. If your DH wants to see his kids at his mother's house, that's his choice. If he wants to book an airbnb, that's his choice. It's simply not your place to tell him not to.

Your statement " problem - what society says is the normal thing to do is to be this one blended happy family. " doesn't really happen in real life. Only on movies and tv.  Do what you can, in the end the kids only have one BM and BF. You are not one of them.  Be careful not to get burned in the end.  They SK loyally will always be to BM 

IMO "co-parenting" is a make believe term made up to help people feel comfortable about failed families. "Co-parenting" only works when both parents are reasonably functional. The reality is that most people wouldn't divorce in the first place if there weren't significant dysfunction on the part of 1 or both parties. Divorce may be common but contrary to popular sentiment, divorce rarely happens lightly. It happens when the family dynamic is seriously f*ed up. What usually happens is Dad's house Dad's rules and Mom's house Mom's rules, not this namby-pamby "co-parenting" that family courts like to pretend exists. 

I set and enforced standards of behavior and standards of performance that the kid met or received consequences.  If my DW did not parent and discipline, I did.  If she did not like how I parented and disciplined she could stup up and get it done before I had to, or she could have my back and we would discuss it in private.

The same held for me if I did not like how she was parenting and disciplining.

We colaborated on zero tolerance in dealing with the toxic blended family opposition in order to defend the best interests of SS and to protect SS and our family from their noxious bullshit.

Though it may sound surprising, or even delusional, we have had a great life as a blended family, DW and I are happy (29+ years married) and SS-31 had a great childhood and is living a good life as a viable adult, a man of character and honor and is a man of standing in his profession and community.

Conversely, his three younger also out of wedlock Spermidiot spawned half sibs by two other baby mamas are each a train wreck.  Spawn#2 is a Dole Queein, #3 is a convict serving a long prison sentence, #4 is not far behind the inmate.  The manipulatie toxic crap by the SpermClan, primarily SpermGrandHag, took focus and the prompt delivery of escalating abject misery with every legal, financial, and social tool we could use.  Ultimately, we won and SS has put the shallow and polluted end of his gene pool behind him.

Marriage is not about giving up yourself for your mate. It is about each of you making the other and the marriage the uncontestable priority and being equity life partners.  Kids benefit from that, they are not a part of that.  Kids are the top adult responsibility but NOT the priority.  

There are countless examples of failed marriages and shit children, when those children are the worshipped priority of their idiot parents,  who grow to be shit adults and have yet more shit children.

A parent's duty and responsibility is to prepare their children for life. It is not to protect them from life.

Take care of you.

All IMHO of course.

Sounds like there is a lot of info missing here. 
1) Did your DH ever have his own place where he parented independently? Where was he living before he moved in with you? How big a role did his mother have in caring for the skids before you married? 2) How many different cultures are at play here? You mentioned your parents had an arranged marriage, BM is Hindu, and DH is Catholic, and you all live in the UK? 3) Are one or more of you "on the spectrum?" You mentioned BM can't help skids with homework and they are very young, and she can't differentiate between emergency and routine. You also mentioned sensory issues.

All these things will make this very hard. People are sh!tting all over you for not allowing DH to be a true parent, but was he ever a true parent? You can't take something away from him if he never had it. You guys should get counseling to deal with these issues. 

For you:

- don't interact with the ex, don't get involved with exchanges, don't get involved with changes in custody schedule UNLESS it directly affects you (example, you and DH already had plans to go out of town and BM springs the SK on you last minute)

For DH: 

- communication should be about the child, and the child only

- both should be signed up for school & doctor emails/records

- any concerns can easily be done phone or email

When DH and I first got married, BM was OBSESSED with trying to "sit down in person" with DH. For whatever reason she felt the need to talk in person and dictate when & where they were going to chat. DH stuck to his boundary and never gave in. He felt it was something "extra" and not necessary for them to communicate about SD. Now that SD is 13, they honestly don't communicate much at all. I would say they "parallel parent", but just google.