well first of all we can't change the alcoholic or drug addict. only they can. nothing we try will work.
secondly, if i found myself in this situation, even with a sib, i'd tell him he has to find another place to live and give him a written deadline. if you live in the states, if you post the time he must leave on his bedroom door, you can evict him legally.(check laws in your state.) you do not have to live in fear for your safety. right now your letting him live with you is enabling him. it rids him of being responsible while he drinks. he won't hit bottom if you participate in allowing him to live there.
hope this helps. i think you already know what you need to do. tough love may actually help him more. you on the other hand would benefit attending Al-anon.