There are people in our lives (mine anyway!) who will push and push until you decide that you've had enough.
Perhaps your parents will cease to be so horrible to you when you make the statement that you have had enough and won't tolerate this any longer.
If doing so changes nothing, then at least you gave it a go. She has no right to touch you in any way.

I would say you're probably at the lowest point in your life right now. Honestly I am not divorced and can only speak from an outsiders viewpoint, but that's what I see.

I really hope that you get to see that the father of your children should at least be responsible for his share of the cost or raising them....get that legality dealt with ASAP...

Rant away here. Nobody minds.
If you prefer, put a disclaimer that it's just a rant and we won't bother you with any suggestions.

P.S. Please take care not to let people diagnose you (your children's therapist) unless you seek it out yourself.