I have tried to have compassion for her and the pain she must be going through. It is the ever changing moods, the lashing out like she does over "things" while at the same time not caring about what should be more important like her kids. I am learning and getting more able to deal with things as time goes on. I hope she never gets as bad as your ex is still now. I do understand I have no control over that. Stinks but we must deal with reality, not what we want things to be.
Let's start with this - can you let go of the idea that your ideas are right and hers are wrong? For example, what she "should" be doing with the daughters? More like she is doing things with them that you disagree with. That the old her wouldn't have done. Etc.
But the reality is that she can and will do them. The question for you is whether or not it's life-threatening or just disagreement.
What your W has done so far is bad enough. Don't be surprised if there's more and more outlandish and deviating (from who she was) behavior. You cannot protect your daughters from her moral beliefs and changes in attitude. You can help them process it in a way is healthy and in keeping with your beliefs.
So let go of the idea of right and wrong as it applies to your W. For now, there just is. Later, she might be a good Christian woman who did some horrible things to her family. You won't know until later.
Compassion is not the same as giving her what she wants. Like a surgeon might look at a diseased body and remove a tumor. Sure, they have compassion -but they rip it out nonetheless. They are looking at the bigger picture.
In your case, you don't need to be aggressive in stance - you don't need to engage or attack. Just be aggressive in keeping your boundaries and you and your daughters will be fine.
You've had enough to deal with Matt. Focus on you and let her deal with herself.
AJ
"Our lives begin to end the day we become silent about things that matter" MLK Put the glass down... "Yesterday I was clever so I wanted to change the world Today I am wise, so I am changing myself."