Depravo said:
It won't do him any good whatsoever unless he wants help.
this is true, you can send him to all these therapy sessions you and your parents can afford, but, taken from experience, if he does not want to change and likes they way he is living right now, he will "play the system" make the therapist think he is all hunky dory, and with him being over 18, you and your family have no control over weather nor not he will go. If this is a very serious condition, I would contact your local police station, or an attorney to seek legal advice to see if there is anyway you can "force" him to get help, but even then it doesn't always help, but it doesn't help to try. Another possibility is to contact a local suicide hot line and see if they have any advice to get him help as well, these hot lines are also for people close to the affected person.
I don't know how helpful this was, but what ever you do, do not give up on him, he has encountered some hardships and has dug him a hole that he can not get out of alone, and he needs the help from his family, and friends, I know you said he has limited friends, if any at all, but maybe that would be the first step in the process of recovery, he needs to find a true friend that cares, and maybe that will help him see the light at the end of the cold dark tunnel he is in right now, and will want to make him seek the professional help.
When I was kind of in his shoes, I talked to a family friend is a great listener and great advice giver, if there is anybody like that in your family, or if somebody knows somebody like that and he is comfortable talking to them, just have him sit with them for an hour or so while you and the family are not in the same house, completely out of ear shot, and just have him vent, maybe he is too afraid to talk to his close family as he is afraid of breaking your love you have for him, I know I was afraid to talk to my mom as she isn't one of the best people to talk to, nothing is ever confidential with her.
If needed I have some other recommendations too, but I'll keep this post at this, if you want more advice, shoot me a PM and I'll try to respond in a timely manner, but like I mentioned do NOT give up on him, do NOT consider him a lost case, and do continue to talk to him, even if it is sitting by him as he is playing a game, or maybe find a two player game that you and him enjoy and just play, even if you don't talk, he will know you care and maybe that will help him want to change. Do not take drastic steps like getting him a hooker (I hope this was a joke) as from the sounds of it he is so deep in the hole that he needs to take baby steps to get back to a happy state of mind, it will be a long and stressful process, but once he is back to "normal" he and the family will be very happy they took the time to make him better.