This is my first real post here, hehe...
I am 18, and I went through a very similar thing when I was 15/16, minus the drugs. I was very depressed, and I could not get up and go to school, so my parents took me to court, I dropped out of school, everyone hated each other, it was a huge mess. I am not a bad kid, and I'm pretty smart, but depression and anxiety can do terrible things to you. My probation officer was pushing to send me to a detention center or a foster home, and my free court appointed lawyer was doing nothing. Finally, a judge stepped up and said that I needed mental help, not disciplinary help. So, I stayed home, started working full time, fell in love, and everything worked itself out. I started high school again last year, at a special charter school specifically for people who have dropped out and need a second chance.
The point of my story (yes, I have a point, I promise) is that I think your brother probably has some mental issues that are preventing him from being the person he normally would be, and he is turning to drugs for comfort. That's a very common thing for kids with depression. I think that instead of sending him away, bring hom closer. Do fun things together, and let him know that you and your family will love him no matter what, and that you're there for him; you're on his side. I'll bet he feels like everyone hates him, and that will not help anyone.
I'm sorry for my ranting, but it's a subject very close to my heart. I'm sure it will all be alright, but you just can't give up on him! Good luck.
