A lot of these maladjusted men will not stand up to their miserable ex wives because they're scared of what might happen (the nut job taking the kids away and lying causing PAS). 
 

These fears sometimes are not real but sometimes they are and could be resolved by hiring lawyers but that is expensive for most people

They know if they stand up (as they should) they might risk losing a relationship with their kid (if manipulative mother is CP) especially if the kid doesn't have a car and can't make decisions well (ex. screw my crazy mother I'm still driving to your house this weekend dad) 

 It sucks and you have to decide "is this something you want to deal with the rest of your life"

the nutjob literally said she will destroy your cozy life with him and doesn't want you around her kid. She meant that. She will make things difficult for the next 18+ years.  she probably is miserable and has nothing better to do than plot and scheme to get her way. 
 

This is exactly how this dude over here's ex wife is. miserable breeders with no life using the kids at manipulation tools because that's all they have. Can't use their looks or p*ssy to get their way so they use the innocent kids who have no clue and can't stand up to these c*nts either. 
 

You're already married and (IMO) in traditional marriages the wife/marriage comes first then the couple leads the kids then the extended family. 

When a man puts his marriage first he will not be controlled remotely by his previous marriage/wife. That's why he divorced. 

The choice you have is to 

1. Discreetly record EVERYTHING and sue her in court before she tries to sue y'all (possibly get more/full custody). Report her for PAS - judges do not like that. 
2. Do nothing and continue to deal with her manipulation tactics as best as possible
3. End it with your husband and find a man with no baby mama drama who puts his wife and marriage first 

I am a little confused.. because didn't you say he went mental at her over the accusation ..and she walked it back?  so didn't he have your back there?

I get not wanting to go into her home.. but it also feels like that doesn't necessarily have to be a huge conversation with his EX either.. can't he just walk them to the door.. let them go in?  if BM tries to talk to him.. he can just stay outside?

It sounds like she is high conflict.. and he isn't looking for reasons to cause more.. so maybe just doing what you suggest.. vs talking about it with her (where she will argue about it).. is best anyway?

Unless she lives in a very dangerous area.. if you or he are able to watch the kids walk to her door. should be fine to just start letting that happen.. 

Our BM used to be similar. I say "used to be" because DH put a stop to it over and over again until she finally fizzled out. She used to email DH lengthy "report card" emails with everything he did wrong during his parenting time - SS had too much sugar, SS stayed up too late, SS did an activity she doesn't approve of, SS was with any family member that she didn't like, etc. Of course, these standards only applied to us, but never to BM, as she often broke her own rules. 

DH constantly repeated that it wasn't her business, which would send her through the roof, but he would ignore her. When we took BM to court in 2019 for her crap, the judge told her that it was none of her business. She tried to argue with the judge and the judge shut her down. That was the end of it. 

Your DH needs to simply put her in her place each and every time she has a "complaint" and ignore any blow up that arises after. The only way to stop the behavior is to stop giving BM the supply and attention she so desperately wants. 

They should be walking by themselves to and back from DH car.  There is no need of communication between. BM and DH. And in this case it should be done by texting. So there's a physical record of what was said.  
'You must step back.. Stop taking SK anyplace by yourself.  BM doesn't like that you are trying to be a mother to her kids.  You are adding gas to the fire. 
DH should be taking his kids, it's his time to be with them. Not dumping them off on you.  If he can't take care of his kids ,then they should stay with BM..  

'DH should stop communicating with BM about anything except the kids.  At 14 he can text her on things like " I'm outside" 'we are going to. Fair, so dress. Warm". Thus not getting BM involved.'

SD can text BM with things like " we will be home at 5". " we are going out fir pizza, so we will not need dinner tonight" Not getting DH  involved 

That the longer skid sees dad suck his thumb around the almighty BM, the faster skid (and SM) loses respect for dad which excelerates the skid PASing out.

The Girhippo in my case did the same thing right out of the HCGUBM playbook.  I refused to be around the 3 ferals alone bc Chef would take the Gir's/skid's word for things over mine after she repeatedly lied to him and he knew it.

I didn’t read all the comments, but I agree with whoever said that this doesn't have to be a whole conversation. Your BM craves attention and your DH gives her what she needs. She shouls be completely ignored unless it's about the childrens' health or education.

Calling about bs, messaging, conversations during pick up and drop off - put your foot down and tell him no more. Calling her out will not do anything good, it will only create more drama and more of BM needing to clear things out with your DH.

When I moved in with my husband, the BM wasn't high conflict, but used to literally text/call about everything. She just couldn't let go of her first lady status. It was "Don't forget to vote today", "A kindle was stolen from my unlocked car, should I call the police", "How do I open a new bank account on my name?", "Do you know any free notaries?", "Do you have extra bread at your house?", "Ss is getting a new this and that", Please change the oil on my car", "Please fix the leaking sink/toilet", "There was a bobcat near our house, are they dangerous?" etc etc. I wanted to scream - Lady piss off!!! 

It all stopped after she refused to let husband's son go visit his grandparents, because "they will cause emotional harm to him". Umm what?!  My husband was furious and decided he wasn't her handyman anymore. He waited until she called him that her car needed service to tell her that she can take it to the shop. She was so wrapped up in herself, she couldn't believe her ears. She cried that it wasn't fair to her LOL

Then it didn't serve to be friendly anymore and showed her true self. She wasn't miss nice anymore and took every chance to passively aggressively remind that she was the only one to make decisions about their son. I had enough of all the unnecessary communication and I put my foot down. After all, my husband kept to his word and ignored all bs messages and calls. All communication went through email and it was only about health and education. Period. He never had that conversation with her about it, he just ignored her for as long as it took her to get the message. Of course she became so petty, she'd email receipts for literally $1.99 requesting reimbursements for prescriptions. All her emails(about once a week) became money claims. That's how miserable she is. I feel sorry for her and the sad life she’s living. 

If your husband wants to take his children out for lunch, he should communicate that with them. Same with pick up and drop off times. His children are old enough to figure that out by themselves or with their BM, no need of your DH to do it through mommy. As for you - you shouldn't be alone with the children. Have your grown ass husband figure it out. Same as if he was single or if you weren't working from home - that's something the parents have to figure out. Remove yourself as much as you can. Your husband is way too much involved in the BMs drama, I agree that he is the actual problem.

By the way his fears soon or later will come true - he will end up with damaged relationship with his children. But that shouldn't be on you. Don't you ever feel guilty. 

Best of luck and hugs.

He's not thinking straight. She threatens to stop him seeing the kids? Yet she dumps them on him when she needs time for herself? He needs to take the wind out of her sails and say no the next couple of times or so to let her know that she needs him and so CANNOT stop him from seeing his kids. He has to take back his power and stop being a grovelling doormat. Have you told him what a turnoff it is when he grovels? That every time he caters to her you lose a bit more respect for him and that your supply of respect is limited? If not, you should.

BM has never worked?  How does she support herself?  Is he going to be giving her money when child support ends?  This woman can't support herself,  does nothing yet can't even get her kids to school.   She's going to be a lifelong burden. 

OP

About BM accusing you.

Do yourself a big favor.....Never, ever find yourself alone with dh's and bm's child. Not in a car, not in the house, not at a playground, not at a store. NO where. 

Then immediatley file a defamation suit. Drown BM in her toxic shit while giving the SKid the full facts and full visitibility of how toxic BM is and how much pain BM's crap will result in BM experiencing.

Zero tolerance for this crap.  

Set the example of viable adulthood and a solid adult relationship for SD. Then execute scorched Earth against BM for any crap she perpetrates.  Do this whether your DH agrees or not. BM is targeting you. Take her out with the full  arsenal  of financial, legal, and social weapons at your disposal.

IMHO of course.