I had it quite badly at university - although not as badly as your brother.
It used to take me 10 or so minutes to leave the house - making sure everything was swtiched off, the doors were in the correct position, nothing was parallel on coffee tables etc (I know

). I used to think that if I didn't do these things then something bad would happen. OCD did help me stop smoking though - I was at a stage where I would have to think of a certain thing while taking the last two pulls on a cigarette. I got SO fed up with it I gave up so I wouldn't have to do it anymore, lol.
I took it upon myself to go and see a therapist (is that a really American term?) and, while a little patronising it helped a bit. To be honest though, she couldn't really tell me anything I didn't know - I knew it was in my head and I knew I just had to stop doing the things I was doing because, really, they had no consequence. She did suggest stopping doing one thing at a time, or checking things one time less, each time, if that makes sense - gradually working up to stopping things completely.
It sounds as though you've taken the first step though in getting help and it can only get better from here.