It is often said that it is a very bad idea to go into business with friends and family. Your situation is a good example. If you had hired a programmer and he did work like your brother does, then you would probably fire him after a couple of warnings. But you can't fire your brother -- well you can fire him as a programmer and keep him as a brother. Other people have done that and once they get over the short-term upset, things tend to work out for the better.

If you want to go down that path, it might be advisable to have a trusted and respected family member to mediate. If there is no such person then somebody independent would be a good idea. But do not try a friend for that role, it would only cause rifts.