What to do about a rebellious teenager?

I've got a friend (matt) who is pretty much a father to his 15 yo brother (James) They live with their parents who own a business and are always working and rarely at home. They have no say in James' life, he just hates them and has even punched his father once. James goes out for days at a time without telling anyone where he is and he won't answer calls from his family. Him and his friends sleep in the park, he does weed, rarely goes to school, doesn't do homework..
James does not listen to anyone, though sometimes he listens to me. I'm quite close to this family so I care for him like my little brother but I don't know what else to suggest.
James' parents employ him at the restaurant that they own, I suggested firing him because he never goes to work anyway. But they're scared if he doesn't get money he will resort to selling drugs
What should matt do?

James has seen a psychologist 6 times and that did nothing for him so he refuses to go back