This may sound odd but congratulations on leaving and staying gone.
It's not surprising that your children are now taking some of the brunt of their father's current actions. Of course they want it to stop, but you taking him back isn't they way to make that happen.
So, what can they do? They need to find a way of dealing with him when he is acting in a way they don't like ---
1. Dad, I'm going to hang up the phone if all you're going to talk about is mom.
2. Dad, I will call you once a day to talk to you but that's all I can handle right now.
3. Dad, I will talk to you once a week because that's all I can handle right now. You know I"m going through my own stuff too with you two splitting up, right?
4. Dad, why don't you write this all in a letter and mail it? Note to you -- don't read the letter. Just pass it along to your attorney.
5. Any texts, voice mail, email, etc. -- Tell your son to not read it, it really is OK to not dive into them/the drama of it all. Or he can listen to/read it all at one time and respond at that time IF he thinks he needs to respond but it's probably better if he doesn't. .
I do hope you're find a counselor for yourself and your 12 yo. Living with abuse for so long (30+ years for you and your 12 yo's entire life!) fills your head with all kinds of junk. Getting help to deal with it all takes time, which stinks but it's true. Your adult kids could benefit from it as well ~~ a family counseling session or two -- without the abuser there -- might be helpful.
Bless your brave brave soul for standing up to an abuser and getting yourself out of the situation. No one deserves to be called names and made to feel worthless ... no one.
Look, bottom line is that people do not change their spots overnight. He is not going to transform from who he was. People can change but it is usually a long, long journey and no matter what, we don't stray too far away from who we fundamentally are. If you go back to him, more than likely you will be in the same pattern within weeks or months.
Time is your friend, not your enemy. Give yourself time and freedom to figure out who you are without him. Maybe he can start on a journey to become a better man ... either way, you will be in a healthier spot.