You've really got your hands full.
Some thoughts - your son is almost 17. He's been "doing his own thing" for some years now. You haven't been able to make him do what he should be doing (going to school, staying off drugs, coming home every evening) so why do you think you could begin forcing him now? Besides, legally - I don't think you could. Check the laws where you are at the moment, but in most countries, someone who is almost 17 is able to take charge of his own medical treatment if he chooses. It's a huge problem with a kid like this when they are uncooperative in so many ways, but the flip side is, a kid who needs medical confidentiality and who needs the opportunity to develop their individuality, has the right to make their own choices. We can't have it both ways and kids like yours now, are the frustrating side of this.
The result - I strongly suspect that if you try to impose your parental will on your son to either get him into a therapeutic boarding school where you are now, or the US, you will find he will be able to refuse and you won't be able to do anything. And the suggested move back to India - it would break his current connection to drug users but someone who is a habitual drug user (which he sounds to be, from your description) will be able to quickly find where the drugs are. Drug users and pushers seem to have an international language.
The other possible outcome - if he doesn't like it wherever he is taken, he is sufficiently independent (certainly in his recent actions) to just take himself off to wherever he wants to be, with whomever he wants to be. So you might move the family to India and find that he either gets back into the drug culture, or he just leaves and makes his own way back to whatever he was doing.
Whoever told you that it's not a learning disability, but ODD on its own sounds like they didn't check things out very thoroughly. ODD rarely is the only problem, you often get it when an underlying problem is not being managed. That doesn't mean it's your fault - sometimes the underlying disorder is just too difficult to understand or to be able to help. It needs a different way of handling and it's often difficult to know exactly what to do.
You say your wife doesn't want to keep calling the police - but there can be a number of reasons why you should. First, if you just let him carry on without consequences (because you really can't stop him, can you?) then it's sending a message to him, to his (currently well-behaved) younger brother and to the public at large, that what your problem son is doing, is perfectly OK with you. And clearly it's not.
And also by not calling the police, you could be leaving yourself wide open to being made legally responsible for any crimes he commits or damage he causes. Again, it depends on the law where you are.
I hate to say this, but currently by allowing him to come back home "to base" even though he is physically abusive, disrespectful, indulging in criminal behaviour and not meeeting his obligations (coming home each night, going to school, staying off drugs) then you are enabling this behaviour and making it MORE possible for him to continue. It means he will continue doing the wrong thing because you make it possible.
While you hope that he will eventually stop the bad things and turn it around, he has no reason to do so. In fact, he has every reason to continue doing what he is doing.
Your fear is that if you say to him, "You do not live here any more unless you start going back to school, stop doing drugs and go back on your medication," that he will walk away and live on the streets as a drug addict and criminal. Then you will feel guilty and responsible.
The trouble is, even if you don't say this to him, it is still a strong possibility that this will happen anyway. And it is HIS choice to do this. You didn't put the drugs in his hands. You didn't tell him to be violent. But the longer you continue to feed him, to clothe him, to make excuses for him - the more traumatised you all will be and the more your younger son will see this and think, "My parents have strict rules but they are powerless to actually make us follow them."
You need to focus on your younger son and support him now. He is being damaged by all this and how you handle your older son will be telling the younger one a great deal.
I strongly suggest you and your wife get to a meeting of NarcAnon and talk to other parents there about what options you can realistically use, to help you cope with your sons. You want to do the right thing by your older son (and do what you CAN, rather than what you ideally want but can't really do) and also keep your younger son on the right path.
One more thought - your son was prescribed medication. It has been said (on this site as well as in many other places) that drug users are often self-medicating (or trying to) for an underlying, often undiagnosed, disorder. Someone with bipolar, for example, can use illicit drugs to try to cope with their moods. Someone with depression can use drugs to dull the emotional pain they feel. And often these drugs can make the problems worse in the long run when the underlying problem is made worse because these drugs are NOT what was carefully manufactured to strict specifications and administered in a carefully controlled dose. All the variation in what they take, the strength of the dose, the quality of the drug - it just makes things worse.
But the tendency to self-medicate shows up in the illegal drug use. Sometimes getting appropriate diagnosis and treatment can turn things around, but you've already tried this and it didn't work for long. It's reached the point where HE has to accept there is a problem and to want to fix it. I don't tink he's there yet, he's having too much fun.
Example - how does he get the money to buy the drugs? Is he stealing it from you? Is he earning his own money in some way? Do you give him money (to pay for school classes, for example) but he then uses the money for drugs? Or does he ask you for money to go out with friends, and then buys drugs with it?
You can make it more diffficult for him, if you find out what you are legally required to do for him until he is 18 and then only do the minimum. The busier he has to be to meet his needs, the less time he has to go out and get drugs. If you MUST keep him housed, fed and clothed until he is 18, then you can set rules - "until you go back to school and make an effort, we will make sure you have a bed, plain food only and simple clothes. Nothing special, nothing fancy. No television, no computers, no mobile phone, no toys."
Some people here call it "do to get". Provide the bare legal minimum. While the child is uncooperative, the parents have to be uncooperative. The more the child complies, the more trouble the parents can go to, to make the child's life more pleasant.
However, I am very much afraid that with your older son, you have reached the point where you can no longer control what he does. You are likely to have to stand by and watch as he spirals further down, until he reaches a point where he HAS to take control of his own life and accept personal responsibility.
In the meantime all you can do is help your other son and keep your problem son in your prayers, but not under your roof. You have to be safe.
Talk to NarcAnon in your area and find out what you are legally required to do, and what you are legally able to do. For example, you may be legally required to notify police every time your son fails to come home or refuses to go to school. Or you may be legally required to keep your younger son in an environment where no illegal drugs are used or kept, by anyone.
One big piece of advice here - no matter how much you want to, you should never try to control what you are unable to enforce. It is better to not try at all, than to try and fail. Because to try and fial sends the mesage to your child that you, the parent, are powerless. That is a very bad message to someone you are trying to control.
It means you have to try another way. And one of those ways, unfortunately, may turn out to be making him leave in order to force him to take control of himself and for you to put your energy into your younger son.
I'm sorry you're going through this. Do let us know how you get on. I'm sorry you need us but glad we're here.
Marg