In your place I would start putting less effort into family life, and also resign yourself to the fact that whatever you do, your stepkids won't treat you the way you think they should, the way you deserve.  You sound like you also need a come-to-Jesus meeting with your husband, who, despite his great love for you, "has turned on you", and will "never stick up for you.".  He needs to start putting you first, but more importantly, so do you.  

Give yourself and them a break from your special efforts.  Focus on you and your bios.  Heck I'd even give DH a taste of less of me.  Turn on you?   That's a hill to die on, it sounds as if nobody has your back.  Time for the 180 , it's where  you focus on yourself, if they want to join you, (your choice ) great but no more bending over backwards to keep the peace or serve them.  You are not a doormat so stop acting like one.  

I am so sorry. That was painful to read, so I can't (well, I can) imagine how you are feeling. First, have you tried talking to your skids (individually) about their behavior (asking them questions)? (I will say that I tried this with SD a long time ago, and she clammed up then posted on social media something about how she wished she had told me off. . . *ok*. . . but at least I attempted to fully open that communication door to "clear the air.")  Of course, I would talk to DH about this, not asking anything but TELLING him what has gone on, what is going on, and how you need to start protecting your own heart, so you will be backing off/backing up. You deserve respect. And, in reality, his kids are disrespecting him by treating you disrespecfully. If there's no movement, understanding, communication with the skids and DH, I'd then seriously back up: No cleaning their damn houses; no special get-togethers for them; no babysitting. None of it. 
I've been through this--not to the extreme that you have--and one day I really had to say "No more." I completely withdrew. I was tired of being treated like crap in my own house. No more gifts. No more cards. No more social media "likes" or comments. Life is much better with DH visiting his skids and the grands outside of our home (I've never met the grands and, honestly, don't intend to). I concentrate on my own family members who care for me and my DH and who are decent human beings, not angry s***-throwing orangutans. 
If this doesn't work at all, I'd suggest couples counseling with a therapist who is familiar with step situations. A good therapist will tell you all that your marriage comes first and will probably help to open your husband's eyes. . .and will suggest that you set firm boundaries. 

It sounds like you are a very caring woman.  It's difficult for kids (of any age).. when they have a parent that is selfishly putting their own bitterness in front of their children's ability to live happy lives.

But.. you say that they treat you nicely.. but don't treat you like family.  I'm curious what kind of situations make you feel this way?  are you excluded from events where the EX will be present?  (which I would be happy to avoid..lol).  Or is it in some other way.

I mean.. the reality is that these are your husband's kids.. and not your bio kids... they may feel they are in a loyalty bind.. and they may just be jerks.. or immature.

Your choice at this point is to decide how to respond.  Perhaps you don't put yourself as far out there for people that don't consider you family?  Maybe disengage from them a bit.. and spend more time and effort on your own bios.. and let your SO step up for his?  You don't have to watch kids or clean house if you don't want.. and maybe that is the route you want to take.  I would hope that you would continue to treat the grandkids with kindness.. because they didn't create this situation.. 

But.. if the kids are treating you nicely.. perhaps accepting your role as "dad's wife" and as such his support system.. and having a friendly relationship with his kids.. is the best that it gets.. and focus on your own kids more?

I'd step back - stop doing things for the skids that you, knowing you'll never be family to them, don't want to do.  And your "wonderful man who loves you so much?"  In my experience, such men don't turn on their spouses and fail to back them up.  Expect better of him, and let him know what he needs to do better. 

When my DH and I first got together/then married, I tried very hard to make the 5 kids a blended family. I treated his 2 boys the same as my 3 kids.  Eventually, I saw that the OSS didn't see me as a family member (I wasn't trying to be a 2nd mother to him) and neither did/does his wife. Approximately 5 years ago, I went Gray Rock with him and his family and it's been a lovely place to be.  DH now makes all the effort and plans with OSS or they don't get made.  Therefore, they don't get made.  DH makes very little effort. I've had to be the one to set boundaries and I'm not afraid to voice them when necessary. It sounds like you need to take the reins if your DH isn't going to man up and tell his kids what they need to hear.  Who cares if you're made to look like the bad guy.  It sounds like they don't respect you anyway.  OSS and his wife brought their youngest to our house one Christmas and the poor baby was sick. I asked him what was wrong with the baby and if it was contagious.  His ignorant response was 'it's a bad cold, it'll build up her immune system.  My oldest daughter (who had 2 little ones herself) said 'is it RSV??" Idiot OSS didn't have an answer.  Going forward, I let them know if either of the girls were sick to please not come.  A runny nose is one thing, what this baby had was beyond that.  OSS doesn't spend much time over here anymore BECAUSE of some of the simple, common sense boundaries I've set.  That's a win for me.

I wish you luck.  As much as I love my DH, I wouldn't have gotten remarried if I knew how tricky step parenting was.

I didnt read all the responses so not sure if this was covered..

Your DH is a total prick if he doesnt stand up for you and even worse has turned against you. Period.

Your problemo lies with him. Thats not to say though that your skids arent the problem, cause they are. BM may have worked them to dislike you, except as adults they make their own choice how to behave. I hate when people excuse rude ass ADULT skids because BM brainwashed them. Nope that doesnt fly as adults...otherwise we will never be held responsible for our own actions. Thats just IMHO.

Id do nothing "family like" for them if they dont treat you like family. Give what you get the same goes for your DH. This life brings out the worst in people. Life aint fun living with resentment.

Id tell your loving DH that he has to stand up for you. If he doesnt stand up for yourself. If your skids treat you off tell them you dont appreciate it. Let em know that you are aware of their actions. Let er rip , thats just IMHO

Blessings hun

Gives you time, to know what you need looking for , in a new counselor.  You have to disengage from this mess of a life . His kids are not going to get better.  They will always be in the middle of drama. Your SO doesn't have your back. He so uses to drama he fits in.'

Disagreement means , not getting involved with SK,  and there drama, if they get thrown out of there apartment , there is motel 6 not your home.  If they have no money. There is welfare. Not you support them. 

Harden you heart and harden your mind.  Life is not about what you hope, it is about what is.

Guage people by their actions and never be fooled by their words.

Embrace those who are quality and contribute quality to your life.  Conversely, you know what to do with those who are not and do not bring quality to your life.

Flush them with the rest of the crap.

You and the people who bring quality to your life are owed your care and love. The crap, deserve nothing.

Take care of you.

Keep doing you, just stop embracing the delusion of what you hope for and embrace the facts.  Make sure that everyone knows those facts.  Facts are not mean, they are not manipulative. Facts are neither good nor are they bad, they are merely facts.

BM needs her cocaine rotted nose scrubbed in the stench she has created. Her kids, need to see that happen and they need to have their own noses scrubbed in any BM related stench that they delusionally embrace.  Your DH, needs to keep his X in her place and deliver clarity to the children he sadly chose that nose candy skiier to be the mother of.

Keeping the facts forward and everyone grounded in the facts, is a foundation for living well for everyone unfortunately having to live at some level within this trainwreck.