If there is a court order for child support, you can file contempt of court charges if he isn't paying. I would ask that the support gets garnished from his wages.

And if there is a court order that states he only gets the kids one day a week (given his addiction, I hope it is supervised), then that is all he gets the kids. If he wants more, he's going to have to go to court to get it.

And he's going to have to prove that he's drug free. Was he tested for drug use at the time of the accident? If so, that is enough to get drug testing and supervised visits.