Hi Qwe ~ welcome back!
I don't really have any advice for you, but I do have a question... is his drinking a violation of the visitation agreement? If it is and you have proof that he is still drinking (the pictures, etc), then that is an avenue that I would definitely pursue. It doesn't mean that he cannot see the kids, but it may mean the visits would need to be supervised.
Even if his drinking is not in violation, I would contact an attorney and find out what can be done. If you feel like the kids are in danger (or will potentially be in danger), then I believe that we (as responsible parents) have an obligation to protect them. Even if it upsets your ex-husband.