You should be very proud that you have taken the first steps to free yourself of abuse. You have a good chance of now avoiding long-term misery, and all of this pain and stress is a very good investment in your future.
Try not to focus on what his parents believe; it is not in your control, and though it may be disappointing, your attention is better placed on you and your boys.
There are many reasons a wife does not leave an abusive husband, and his needs, his responses, are large parts of that. Switching gears to your needs and feelings may be difficult, but if you try to remove yourself from his head, you may feel a little better. It sounds like he dominated your thoughts and feelings for twenty years, and it will take effort to start considering what is best for you, and not think about how it affects him or his family. The fear will not go away immediately, but will ease over time.
Your boys are almost adults, and it is important for them to understand that their father uses fear and rejection to manipulate and control others, especially his family. Abusers rarely admit their abuse. People who harm women and children hardly ever confess. They know they are the lowest of the low, and he's probably smart enough to know any admission can still land him in jail. These days, a microphone can be hidden anywhere, and I would bet money that he's smart enough to know that. Please let your sons know that he will never admit it. Sometimes, on their deathbeds, abusers want absolution, and will confess then.
You are probably not the best person to counsel the boys, because you are under so much stress right now. It seems like it would be nearly impossible for that stress not to spill into your conversations with them. There are mental health services available in most cities, based on income. There are also free support groups. You can search online for resources.
You didn't say if you ever sought emotional support from a professional. If not, finding a counselor to help you sort through this may be something you want to try.
As for a job - you don't have to start "big." Just get out there, and face the world. Easily said, harder to do, I know. Smaller cities may be more comfortable. It will also demonstrate to the court that you are willing to carry your share, that you are trying to financially contribute.
His cheating has little to do with you. Cheaters cheat, abusers abuse. I'm sure you heard the word "you" quite a bit if you confronted him, as though it was all your fault. If you haven't confronted him, there is really little point to it, except to be the recipient of more abuse.
I don't think it matters whose name the house and car are in; unless there's some monster of a prenuptial agreement, legally, it should be considered joint property. I hope you have an attorney. Even though it's very stressful, and easier to just want to cut off all contact with him as soon and cleanly as possible, this is not a good state of mind to make big decisions. Maybe your parents will help with an attorney, or know someone?
I would ask that you remember that you survived twenty years of his abuse, and you can survive this. The world will be a much lighter place without his hatefulness in your life.
Do nice things for yourself; take a long bath, do your toenails, change your hair, wear make-up to the grocery store just for fun. Go to the park, plant a little basket of flowers. I like the sound of water - maybe get one of those little waterfall machines from the flea market. I like flea markets, too. People and puppies, good things to smell and always something surprising
I'm sending good thoughts and safe hugs your way.