First off, I am so sorry that this has happened to you but I would also like to mention that a lot of his behavior is definitely not particularly a symptom of depression but being a brat and incredibly inappropriate. Even at my worst state of depression I would never harass anyone and I would very rarely even have the energy to get angry. It seems like you're taking a lot of steps to try and instill some sort of social functioning and discipline in his life but unfortunately it doesn't seem to be working. The above people are correct in how lovely you guys are to try so hard and you most definitely need to look for more support. Support groups are a great idea but I would also suggest talking to friends, family, and even some teachers. Great ideas can come from unexpected places

And last but not least, it's also important to realize that even though you all want to help so much, sometimes you can't. You aren't the right person or it's just not the right time, whatever the reason, a lot of the time, family can't fix the problem for a person. It comes from the outside. Through experiencing the world in a different way and then feeling the change in yourself. I would actually suggest sending him to a camp of some sort? Get him out of his normal environment and it gives everyone, including him, a break from stressors. Send him to a home stay in a different country or let him live with relatives. Something that forces him to stay busy and moving with a firm hand and a gentle heart. Maybe he can be a farm hand for a while? A lot of the time when you are forced to open your eyes, that is the only way to realize your eyes were closed in the first place.

I can tell you all really care for him and that's so great. Don't loose hope, there are still many ways to help him