I don't bring up sd17 and never talk about her even if Dh does. I nod my head or say things like "that's good." I don't give my opinion anymore, it's too much effort and I'm always the bad guy. Or he will in turn say "your kids do this..."
Like you OP wheN she does grace us with her presence I am busy in my garden or craft or whatever. I try not to be around her in a small room.

The only survival skills I really needed, had to do with BM; SD was not a bad kid.

I made sure I had very little contact with BM (practically none).

I made sure that I knew the law inside and out so that my husband and I knew what BM could and couldn't do. This put the power back in DH's court, even though BM thought she had it all just by giving birth and having custody.

The biggest thing had nothing to do with any skill that I had. My husband refused to let BM manipulate him and when SD tried it, he shut her down, too.

Now that SD is 23, we have no contact with BM (although SD lives with her). But my husband worries a lot about his daughter (she's not real bright). So, now I listen to his worries and try to be emotionally supportive while reiterating that SD can never live here.

Mine are here FT with little to no relief. Here are my coping mechanisms:

1- Concentrate on being happy with myself and knowing that despite having a fucked up marriage, I have a really nice and exciting life and am blessed in many ways.
2- I always keep a few things "just for me". Innocuous things are little shopping trips and secret interests that hubby doesn't know about. Big things are occasionally smoking a bowl when he's not paying attention.
3- Remind myself that my SKids are lazy and entitled, but not to half the degree of most of YOURS!!!
4- Rejoice that BM seems to now mostly be put in her place, and DH is finally starting to get it.

Edited to add #5- Overeating. I overeat a lot.

1. Not allowing love to make me stay in a situation that isn't good for me(health, emotional or financial)
2. Not being afraid to address/deal with SKs, BM when they step out of line.
3. Never giving up the ability to support myself. DF knows I won't be think twice about walking walking away from him if he his kids and BMs become too much for me to deal with.

1) Speak up. DH can't fix it if he doesn't know my head is about to explode.
2) Never assume DH can tell my head is about to explode.
3) Sometimes, be more subtle. Let him discover on his own the disaster that's about to fall on SD15's head if he doesn't take action.
4) Speak with authority to skids when necessary. I have my Scary Lady Voice and I use it when I need to.
5) Always, always, always remember that none of it matters if DH and I are not solid and bubbly happy with each other. Nurture that no matter what. Cuz there's no reason to go through any of this if we aren't sprouting sparkles and roses and confetti toward each other in our hearts.

Year One: A combination of my way plus a whole lot of doing it his way because he asked me to. Nearly killed me.
Year Two: My way all the way. I earned it and he has acknowledged so. He's doing it more and more my way, too.

Things with ss13 and me couldn't be better. Things between sd15 and me were only worse when I was doing it dh's way. I've come to accept she may be a lost cause. But DH has really upped his game with her - I have some small optimism about how that may turn out.

I did walk on eggshells for awhile that first year. Partly because I was in shock, partly because DH basically asked me to. But he didn't really realize that's what he was asking me to do. He just wanted SDthen13 to rise to the occasion and asked me to keep "giving her chances." By the end of the year I was a shadow of myself. I didn't like it. I took action. Several months later, things are much better for me. They're not so good for SD15. She's miserable and piles more misery on her own head every day. Nobody's doing but her own.

Amber waves of grain.

Beer. and chainsmoking- but not all the time. that's only when yss is acting up. which is all the time. ok, nevermind. chainsmoking all the time yss is home.

aside from that, my biggest survival skills are:
- fantastic, open communitication with dh.
- always *assume* the positive about your dh, and vice versa; things work better if i dont assume dh has done x,y,z, and better if dh doesnt assume thing about me (like 'u just hate my kids')
- be sure of yourself and decide in a very firm manner what you WILL and WILL NOT choose to be responsible for. and stick with it until you feel otherwise.
- be flexible. kids grow, relationships mature, time changes the landscape of what your family will look and feel like. i never thought i'd have a better relationship w/ oss than yss. but it's actually the complete opposite. as he got older, the dynamic between oss and i has changed and it's rewarding to 'go with it' and allow it to evolve.