You’re asking a loaded question, that should most likely be answered by himself through the help of a therapist. What is your interest in this question. Is he planning to listen to you? It sounds like you want to know how to advise him. Make sure you should be doing this. It’s a big responsibility to break up a family.
That being said, you stated many vague comments/generalities:
1) she is horrible. How? What does she do?
2) he will never see the children and will have nothing but the clothing on his back. He owns nothing? Is he working? How do you think she could legally get away with denying him visitation rights? Unless he’s done something horrible that she can prove it might be hard for her to deny him any visitation.
3) the children are being brainwashed by their mother to follow in her sick ways. Brainwashed makes it sound like they “see” her side of it over his. What are her “sick” ways??
4) what are these threats that prevent him so effectively from seeing his family?
I’m not saying that abuse of a wife towards her husband doesn’t exist, but you haven’t provided any concrete information that sounds convincing that she’s donne anything egregious.