I'm sorry for the pain he's putting you through.
I'm having a hard time reading all of this with no breaks so forgive me if you mentioned it, but have you sought the advice of a lawyer yet?
Your WH and the OW have bonded over turning you into the enemy. As hard as it is, it's time to pull away emotionally. Read in the Healing Library > BS FAQs > #11. It's called the 180 and following it as closely as you can will help you detach emotionally.
Only communicate with him about the kids and finances. Keep it business like. Use email and texts so you have time to consider what to reply to and what to ignore. So you can collect yourself and come here (the Divorce and Separation board has lots of good advice and support) before you answer.
Block that skank from your girls' phones.
And get a good lawyer. Immediately. "Being in love" first moved them to promise fidelity: this quieter love enables them to keep the promise. *CS Lewis*
❣I hope my issues don't discourage ur healing. I've buried a lot & my WH hasn't done his part in R❣