First boundary I would set is no using cocaine in our house around the kids! If he wants to use cocaine make HIM go to the hotel room. Why should your children be exposed to that kind of lifestyle. He is doing irreparable damage to them!
Boundaries have consequences. So the second thing I would do is tell him what will happen if he does use cocaine in the house. I would tell him that I am going to call the police and have him and his illegal drugs removed from MY home.