Either put a COMPLETE stop to the son being in the house at all, or give some anonymous tip somewhere. I ain't sure where. Thing is, if one says "okay, you're out, well, come back but only for today, out again, oh, no place to stay, well, only a week" and so forth, it ain't good for oneself the same way one shall leave an abusive partner completely and never go back.
Parents have a tendency to see their children as "saints", no matter what heinous acts they commit. One CAN break family bonds and put rules for ones own house. I do think the son needs some place to stay (such as a drug home thingy) to not just keep falling and end up at the hard pavements outside. There has to be something to do or say to convince the father the child needs to be helped/pushed back.
If nothing else helps, it is better for a child to grow up with one parent only instead of in a house with a drug involved. Yes, if you are in a situation where it's possible for you, you could leave them all. I know that it does not seem fun at all, and alternative ways are better.
Once again, good luck!
