I was reading your post the other day and I almost replied just to offer a warning that your brother might begin to have doubts about rehab.
Personally I would try not to get too upset. My husband went through this stage also. I think it is kinda common. For me I know it seemed like it should be a simple choice for him to stay, but after I talked to his primary doctor about it, then I began to see it more from my husbands perspective.
No matter how much a person wants to be clean, it is still a difficult process. It is unsettling, strange environment with people you don't know, rules to follow, loss of freedom, loss of control. The body is still dealing with effects of the drugs, therapy sessions bring out feelings, and the loss of the drugs allows these feelings to be felt! It is not easy. My husband was in a fairly lenient and what some would call a "plushy" rehab & he still had complaints.
It passed with time. Although be did get hit with it again later- thinking maybe he was ok and didn't need the whole amount they suggested. Again he stayed. He completed it.
In my husbands case, I tried my best to support his recovery efforts. I communicated with him regularly, went to see him, took our little boy. I wanted to see him, and I also wanted him to realize he was a father, was doing this for himself, and to end up being the man & the dad he always wanted to be.
I found it best to stay calm, acknowledge the discomfort but point to the ultimate goal. I tried to stand firm with my own beliefs, and remain consistent with my actions.
If you do go visit, I would suggest checking with the rehab to see if they offer any special family sessions, or the use of a therapist. I never did outside meetings, but my husband's rehab assigned me a therapist and she was a great help. She explained all about the addiction issues, my husbands treatment plan, helped me work through my own issues. She was my go to person during his time there.
Will send up a prayer for you and your brother - "may his feet stay on rehab ground....."