What's in the best interest of your children?
Personally, after all he's done, I'd have to see at least 6 months continuous recovery for visitation.
I would not take the boys to see him in rehab.
I had no visitors in rehab except my parents, once, and you know what? It was good for me because I got to feel the pain of knowing I had hurt so many people.
What he wants in rehab from you and those kids is irrelevant in my humble opinion.
I would also highly suggest visitation in a neutral location. Your home should be your safe haven, your safe place.