Hey VTSister -
I've been in an almost identical situation. We housed our dry but alcoholic brother for 2 years. He was a daily and copious pot smoker. And then it was just too much of a problem for so many reasons.
In the past, my family has a bad track record of looking out for each other. And I've realized that I was sort of trying to correct that history, in a way. But like you, I really thought my brother would begin to help himself. And that did not happen.
I think all of the suggestions above are good. I think you are being well-intentioned (obviously) but that in effect, you are enabling your brother to continue to be dependant and blind to his true problems. I know it's hard. I had visions of my brother homeless (which may still come to pass) and cried a lot about it all before I could let go.
I know now (with some emotional distance) that not allowing him to stay with us any longer was absolutley the right thing to do. Hang in there.