So,

How do I get my brother to value himself, and not just his son (yes his son is an only child). To do things that HE enjoys, to eat healthy food for HIS sake. I think it's great that he and his wife are such good parents but it saddens me that my brother has totally poured everything into his son's happiness and nothing into his own. If I gave him a gift certificate for his birthday, he would hand it to his son. If I gave him and his wife a gift card for their anniversary for a restaurant, they would let their son pick the restaurant and take him out.

There is absolutely nothing wrong with putting your child first, but if you live your life ONLY for your child, that is pathological.