I agree with Tiffany S. If he's been hearing and seeing these beings for a while, he probably does see and hear them. There are people who have these gifts. It's called Clairaudience and Clairvoyant. There's nothing wrong, per se, with these extrasensory abilities; I have all of the extrasensory abilities (there are 4 of them). Like Tiffany said--your son is in control. He can ask them to go away. He can tell them he's busy right now and they'll have to come back later. He can tell them he only has a one-hour window open, and when that hour is up, they have to go away. However you/your son want to set it up. However, if they've been hanging around now for a few years--they might not want to listen.
If your son really does have psychic abilities, seeing a doctor and having him put on meds will not make the voices or seeing the people go away. In fact, it could make things a lot worse (pharma drugs could alter your son's brain chemistry, which then would make it easier for bad entities to come and visit/use his body. Seriously. I'm not making this up.).
I'm a little concerned about the fact that he has a bad person, Lagoon, telling him to hurt himself or Lagoon will hurt him. There is such a thing as bad entities; the good entities are okay and won't harm you; the bad entities can.
My advice to you would be to find a spiritualist church in the NYC area and ask them for help and guidance. They will be able to tell you for sure if your son is psychic and, if he does indeed have bad entities who are trying to/might harm him, they can help get rid of the bad entities. While as adults we know/are aware of what these supernatural entities can and cannot do, that they can only harm us if we let them--a child doesn't. It can be scary to him that these other beings are always around, even when he doesn't want them around.
Supernatural beings like children because children still believe in fairy tales and goblins/ghosts and make-believe friends. They haven't closed the door yet on the fact that there are other worlds/dimensions out there, making it easier for supernatural beings to come and manifest/visit them. However, children aren't capable of being able to handle these types of spirits without adult help. That's why I urge you to seek spiritual help for your son.