I think you should send his pic and your story in to his new mortgage company...see what they think about what they've just signed up for!
It might be worth it for you to trade with him: you'll resend all the arrears that he owes you and he forfeits any rights to his kids. IMO, it's not worth the boys knowing a loser father who gets them into physical danger when they are with him, and is probably doing emotional damage at the same time. Just a thought.
Hey Ian, I'll start cutting LOTs of paper with my scissors to get them nice and dull