You are in the right place. Search this site for Grey Rock and Disengaging; also the Adult SK forum. There is another recent post on the topic (can't remember the title) but should be easy to find.

Me? Married DH 17 years after 18 months of dating. He had a mix of 3 adult and 2 teens at the time, along with a mentally ill ex-wife who practiced Parental Alienation (PA) at mild to moderate levels. Regardless, it did it's damage. The BM has since passed but after CS ended, she was never an issue. It was her adult kids, who had been deeply impacted by her crappy behaviors.

I tolerated BS treatment for 12 years until the final event that sent me over the cliff. I disengaged completely from all of them for 5+ years. This past year, I have been in contact with 3 of them; one visit went decent but awkard; the other, not so well but boundaries are set and if DHs kids can't abide, then they don't come here. He sees them away from our marital home. 

We are aging...so DHs kids will need to come here to see him in the near future. My plan? Grey Rock. Civil and superficial. I'll offer drinks, a few pleasantries and excuse myself to another part of the house, my garden or my studio. DHs kids come here to visit him, not me. I am not family...was denied any part in the grandkids' lives...so I owe nothing more than civility to any of them. I don't not spend any money on DHs kids or grands, nor do I keep up with anything about them. My life is with DH. We are fortunate that DHs kids are all long-distance but one. And that 30 year old man couldn't even visit his dad on his 70th birthday. SMH

We are also fortunate that my two bio kids are very active in our lives, especially with DH. 

So...with my story....I suggest you look to see if there are techniques you can use to help your situation. Others will also post their techniques. I know you will get some help. Best to you.

Time for a come to Jeusus discussion with  YOUR husband.  He is  YOUR husband which is significantly more important and the uncontested priority above being SD's daaaaaaddddyyyyyyy.

Make sure he understands that. Also, approach the conversations from a "How can we make this easier on poopsies and ourselves to prioritize our marriage, each other, and make sure that SHE understands the dynamic involved in behaving appropriately towards us and our marriage?"

My one had a wife that pushed for kids on deathbed, via IVF nonetheless, and told him she expected him to raise them on his own. 
I didn't think that her ghost still haunts us, cause kids don't even remember her much, and my boyfriend (we don't live together and aren't married thankfully), but I'm starting to wonder now, as I'm sitting in an apartment on holiday from hell. The kids are tweens/teens, they've always accepted me and seem to have a better relationship with me than their father, but they have massive issues (ADHD and ASD), that got diagnosed after I got involved, and there are endless violent meltdowns, tantrums even with meds. We will need to ask for meds to be reviewed. They seem to be joined at the hip and hate each other's guts at the same time. 
 

At the moment I'm feeling really trapped, as the holiday began with 8 hour car trip that was pretty much relentless screaming, then refusing to get in the car after short stops (one was dead serious that he'll hang out there by himself while we go for a hike, mind you, both are in classes for academically gifted kids and play team sports), and now I'm in this hideous costal run down little town that looks like it has drug problems. And I have beautiful home in a resort town also, so I don't know what I'm doing here. 

Apparently the dead BM and the spawn used to love coming here. But she was also a leech that grew up in a welfare family, then nabbed herself a husband that was high achieving and in the corporate world. So this might have been her idea of a holiday. 
 

Fights are continuing, between the spawn and between them and my BF, I finally decided to disengage and told him that he is welcome to go on holidays with them, I will go on mine, and him and I can go on occasional breaks together, but that I will never have a joint holiday with all of them, because my sanity is dear to me. 
 

Thankfully, true to his nature he apologised and agreed with everything. I'm stuck here for another week and am planning to drive myself to various other places that are further out, but are known for beautiful waterfalls, hikes and upmarket eateries, unlike this trash infested town.

You and DH has no control to what SK do, or don't do.  DH must have your back. He must realize what his kids are doing.  He has to pick a side. Or not picking your side is Picking the SK side.  DH has to out you first, if SK come to your home they must show respect to you.  Or else they don't come over.

DH must realize this is the way the kids are. No matter what woman is in the picture it's going to be the same.  The ball is in DH court. 

An epiphany on your situation. You do not have a family. It is arguable that you don't even have a true marriage. Your DH'ss shit spawn are adults and irrevant.  You need to live your life with that clear message front and center to your DH and to his shit spawn.  Daddy is your DH. That trumps shit SKidult spawn. Period. Dot.

A family does not exist just beause a single person is excited about it.  It exists because the adults at the center of it are commited to each other and their marriage and any children are held to standards of behavior and standards of performance. Something your shit spawn SD has never had her nose scrubbed into forcefully and regulatly enough to keep her in her place.

Time to tell daddy DH to grow some balls and put his piece of shit daughter in her place and if he doesn't you will.

Then do it.

Life nor a marriage are something to live in misery because you have already invested so much misery into it. Time to immediately start living YOUR best life and if that makes shit spawn miserable, bonus.

Time for DH to know that YOU are his wife and YOU will not tolerate his passive aggressive shit spawn with mommy issues to further be a detriment to your life's happiness or a detriment to YOUR marriage.  Playing wall flower hasn't worked, so stop being a spectator in your own life of misery, commit to yourself to live your best life, then live it.  DH an man up, or you will live it despite his lack of testicular fortitude. No need to divorce, just go full frontal zero tolerance and  bring the pain to SD and her Daddy when the are being detrimental to you living well.

Assertive confidence with clear standards of behavior and standards of performance that you require from your mate and anyone else in your life solves these things very quickly and with far less drama than people tend to build up in the minds before take action.

Take action.

Take care of  you.

Live well.  Make sure DH knows that you want him to live well with you and you expect that from him as your husband.