UGH! I know from experience that dealing with a narcissistic ex can be really trying. My kids are older but my youngest, in his mid twenties, isn't speaking to his dad at all right now because of it. I don't badmouth my ex either but sometimes it's hard to find an explanation for ex's behavior (I fall back on "well, he had those concussions you know" sometimes.)

Just remember that anger is guilt turned outward - from the vicious way he has always behaved towards you, I imagine he has a boatload of submerged guilt. Plus now frustration that the kids won't fall in line with his fantasy.

Do you have a sense of why S12's grades suddenly dipped? Sometimes it can be as simple as being a little disorganized and getting behind, then getting overwhelmed with anxiety about it. Or he could be getting bullied in school or some such. Or do you suppose that the announcement about OW's pregnancy sent him into a tailspin?

Put the focus on your kids, and just give Ex what you have to give him to keep him off your back. Continue to stick to the high road but don't waste any more time thinking about him than you have to - he's not worth the energy. Document everything and put on a fake smiley face when you have to deal with him. Put nothing in writing that isn't super polite.

(Lol - just thinking about the fact that my ex is always super polite in emails - in a nauseating, suspicious way as he's stabbing me in the back. But in his mind I'm sure he thinks he's being SO polite and kind! I'm sure your ex can't deal with the fact that his actions have upset the kids, so he has to put it all on you. )

Take care of yourself, document everything with the kids, give S12 some extra lovin (imagine how stressed he must have been hiding that stuff from you) and walk him through how he can get out of this hole. It happened to my kids at that age too, even before anything went wrong with my marriage, and I always remember what one teacher said - better for them to have failure experiences in middle school, where grades don't count, than in high school. Better to learn those lessons at this age.