-why not enforce some basic boundaries. Take a good look at a lot of the criminals out there. Do you want your kids to end up being like them? You may think, "why should I enforce rules? It's useless since they're with CP BM 80% of the time anyway." I say: you want to be able to know you did all you could to prevent your kids from being criminals. Even if they do become criminals, you want to be able to truthfully tell everyone you did your best. You should want to give your kids a fighting chance.

-why not play a board game or do some other fun activity with them each for 1-on-1 time? SM might say that she resents you going off and doing things with your kids, but what she really resents is you allowing them to treat her like crap. If you stop doing that, and start enforcing consequences for rude behavior towards the two of you, I can guarantee you those feelings of resentment of you going off to do something with one of your kids will decrease dramatically and become bearable because SM will know you're listening to her and backing her up. That way, everyone gets some of what they want. I can guarantee you that there will be much more peace in your home if you start enforcing basic civility towards SM and replace the guilt-parenting with doing something fun with each of your kids, like playing Scrabble or Chess.

-why not have discussions with your kids about the changes that have taken place? Do tell them the truth in an age-appropriate manner. Kids are smart and hate being lied to. Do let them voice their feelings about SM, but in a polite way, meaning, don't let them scream, "I hate that b*tch!" Instead they could say, "I'm having a very hard time adjusting to SM. What should I do?" You wouldn't want SM calling your kids derogatory names, so don't let your kids call her derogatory names either. You can use this as an opportunity to teach your kids to vent their feelings in non-hurtful ways.