Let him try it. It has a safety net. Until these people see what he is and isn't capable of he simply won't get whatever services are needed.
Let him try it. Until HE tries it HE won't understand what he does and doesn't need to do. He also will be less likely to accept help unless you let him go and try things.
also, he NEEDS to be OUT of your home. He is a danger to you, simply by selling drugs. With the partial set-up, if he gets caught with drugs YOudon't lose your home. and yor parents don't lose theirs. And YOU don't go to Jail for drugs, uprooting your younger child's only chance at stability.
If you ahve a better program or option in mind, then go for that. But if you don't, you are just going to have to let him try something like this. IF he gets to be 18 they won't be offering him any choices. And then you will have an even harder time getitng him out of hte house, or dealing with his rages and abuse.
I am really really worried about you. I know you have to do what you think is best. But he won't ever stop unless he realizes on his own that he wants to stop. This may show him how much help he really needs.