Sasha, I'm going to recommend a book for you, called "When Dad Hurts Mom." It's another book by Lundy Bancroft (author of "Why Does He DO That? Inside the Minds of Angry and Controlling Men"). The book is specifically aimed at helping kids recover from the effects of witnessing violence in their home, but a lot of the stuff that abusers do, in terms of trying to undermine the other parent and to use the children as pawns to continue the abuse, would appear to be relevant to what's going on in your situation.
I have a ton of respect for Bancroft, and I think the book might help you with ways to talk about what's going on.