1) A "family doctor" often isn't savvy enough to handle the behavioral, psychiatric-biochemical, and family issues involved.
2) The boy's problems could be anything ranging from chemical-imbalance-induced hallucinations (i.e., schizophrenic) to well-hidden scars from abuse by the family.
3) My parents, for example, might have helped be get prescriptions from a family doc... but would never have wanted a really gifted therapist to make a good connection with me and uncover the ^%$@$ really going on in the family.
4) To all appearances they may "love him to bits"... but so did my sexually abusive father... and he was a psychologist (so of course *he* couldn't have anything to do with my problems

)
5) The whole family might need therapy. ...and also might be very averse to it.
6) Sorry: it's really hard to guess how to be helpful. But it's super hard to guess (from the outside) what's happening with him or how to be helpful. For one last thing: why does he not want to take the prescribed antidepressants? Because hallucinations are telling him not to? Or because he has genuinely been harmed in the past by his "loving" parents - and has reason not to trust any "help" coming from their choice of doc.
Whew! what a hard place for *anyone* to be in - and for anyone to try to help. I'd be putting them all on a prayer list.
Anybody else got ideas?