I am a recovering alcoholic/addict who is also a substance abuse counselor for adults on probation and parole. I can offer my experience strenght and hope to you by sharing a few things I have learned (the hard way). First, for your mother. The best thing I can ever, ever, do for my children is to give them a sane, sober, emotionally healthy mother. When mother collapses............children loose hope too. She needs to get help now! I turned to alcohol as a solution to problems with a child that were beyond my control and believe me. I made it much worse. Al-anon is a wonderful resource for her and will also help her understand the steps it will take for her son to recover. By working them and putting them to use in her own life, she will see, and pass on the miracle of them to her son. She will also understand the battle he is going to face to change his life. Our problem is not drinking or using, that is our solution. Our problem is our thinking, actions, and perceptions. If she is full of faith in his recovery, it may help him have faith too. If she is hopeless for him, he will feel hopeless as well.  
Jail time is sometimes a very good thing believe it or not. It gives us some time to clear our head and look at ourselves, hopefully. The problem will be getting out. My advise to you is to write to your brother, be honest with him about how you feel. That you love him and will support any recovery efforts he might make but that you love him to much to enable his self distruction. Explain that you have no wish to force your will on him and that you will respect what ever decision he makes for his life but you will not participate in them, if they are destructive instead of constructive. Send him a soft cover AA Big Book, NA book, and some daily meditation materials if you can.  
Be positive and do not ever think that God can't do miracles, because I am one and there are thousands and thousands of God's miracles all over the world. Pray for your brother, prayer is extremely powerful and is often the very best thing, (not the last resort) that we can do for someone. It will absolutely take a miracle for your brother to recover but don't you think for one moment that it can't happen. If you want proof, go to some open meetings of AA or NA and start hearing some of our stories. You will not believe it is even possible that we could be as bad as we have been and our lives can be turned around 180 degrees by a higher power that absolutely loves alcoholics and addicts.  
I hope this has been helpful to you and your family, never give up hope, your hope may be what gives him the strength and courage to have hope too. Don't enable him, offer him your love and support if he choosing recovery, and your love (from a distance) even if he doesn't.