My brother has been full-blown AIDS for a long time. He has started the wasting syndrome process. He recently was in a car accident and received severe bruising and several cuts. My question is how difficult will it be for him to overcome the damage to his body when he has such a small amount of antibodies to fight infection?

Wound healing is impaired in general in people with poor nutrition, but other than that aspect, your brother's HIV disease should not get in the way of his healing from injury. HIV+ people actually have a lot of antibodies, usually an abnormally high amount, but have trouble making antibodies to new germs that haven't encountered before. Since most people have plenty of antibodies to skin germs, I don't think this will be a big problem. It will help if he can keep his nutrition up.