Does your brother respond to a reward system? I have a younger sister who is mentally disabled and growing up she responded well to a reward chart. We just made a chart of what she needed to do, brush teeth, make bed, etc. and she'd get a happy face for each task she accomplished. After a certain number of happy faces she would get to choose her reward from a list (never anything of monetary value) it was sometimes silly things like she could listen to one song on her radio as loud as she wanted, a bike ride with the sibling of her choice, a board game or book....things like that.
She also was stubborn and strong and it was a lot of work to get her to comply with simple instructions (things she was very capable of in spite of her disability) and she responded very well to the rewards.