A woman in my Al-Anon group and a former addict told us that the hardest thing she ever had to do in her life was to ask her son to move out. They had had a deal: he could stay with her as long as he wasn't using. After finding bottles under his bed, she told him her findings and said: "You are jeopardizing my sobriety. You will have to leave as we had agreed." She told us that this was the hardest thing she ever had to do in her life. Within a month of leaving his mother's house, her son went into a recovery program. Now, I can't say that this will happen with your brother. But I can tell you that by enabling him, you are taking away even the smallest chance that it might.
A really good book I would recommend: "Addict in the Family" by Beverly Conyers.
Whatever time frame you pick, you must stick to it. Doing what's best is hard sometimes and takes courage. It may also be helpful to go to some Al Anon meetings to find some more support.