Physical safety needs must be the first priority. Hitting you is NOT an acceptable thing, have you filed a police report?
I KNOW, firsthand, how unbelievably hard it is to turn your own child into the police. but in the long run he will learn that hitting gets you a stint in jail. This is what happens to adults. If he wants adult priveleges (sleeping all day, staying out all night, whatever) and wants to ignore his school responsibilities, then he needs adult consequences.
it really sounds like drugs are a part of it. Or severe instability mentally. He may need a new psychiatric evaluation to assess his mental health. It may be that ADHD is just the tip of the iceberg, or it may be something else entirely. Many of us, if not most, started out with a diagnosis of ADHD. Then we found that there was more going on.
You only have a few years to legally get this done. After age 18 he cannot be forced to undergo evaluation. Or treatment. But it may save his life to force the issue.
If the grandparents want him, let him go there. It probably won't last, but it might actually work. My oldest lives with my parents. It works. But they are retired teachers.
I cannot advise you strongly enough to call 911 the very next time he hits you or rages at you. Ask them to take him to a mental hospital if you think his mental state is part of the problem.
Hugs and all the support i can send. No matter what you choose to do. it is incredibly hard to parent our kids, and I fully understand that I don't know the entire situation. So whatever choices you make, remember I care and support you.
Susie