I feel your pain. I do not like it when control has been wrested from me. And XWH asserted his control over our children in many ways that I could do nothing about: introducing the OW before the D, telling the kids she'd be their stepmother before the D, getting engaged before the D, and then getting married one month after the D was final. It sucked. It set me way back emotionally. When my kids were confused and hurt, I was filled with rage.
On the advice of the members of this board, I stayed fully NC about his piss poor decisions regarding the OW. I emailed with XWH solely about kids and finances. When he'd try to lecture me because he knew that I was speaking honestly with the kids about the D, he got crickets from me. It was so hard. I wanted to send him emails riddled with curse words and put him in his place, only it would have been a waste of time and energy because he didn't think he was doing anything wrong.
Now that I'm used to it, though, I can see that it was absolutely the right thing to do. The kids aren't growing up in a hostile environment (well, not at my place). I feel more at peace because I don't stir the pot-- if he wants to make a jackass of himself and try to lecture me, well, have fun with that. I want to live a happy and drama-free life, and I know I won't achieve that if I respond to his uppity missives or try to lecture him over his crappy decision making.
Anyway, go NC with the MOW (which stands for malicious, overbearing witch). She loves the drama, wants to prove that you're the bad guy, and likely gets her jollies from riling you. Leave her to your STBX. They'll destroy each other soon enough.