That is a hard one. On one level it seems reasonable to say "prove you are sober" to protect your kids. On the other, well, he could refuse, fight in court to have access to the kids and most likely win because a father, alcoholic or not, has rights.
What would his attitude toward this be? Would he cooperate or refuse? If he's likely to refuse, unless you get it court ordered I think you are going to have to give up on the idea.