There isn't much you can do except to talk to your parents. They ultimately have to lay down the law with your brother. It's not your job. He is obviously afraid to grow up. He has no right to order his parents around - that's manipulation. He could end up doing the same for any girl he decides to date.
Wow, that's terrible. I'm in a similar situation. My brother, 25, recently graduated from college but is still living at home, and he's extremely disrespectful to my parents WHILE free-loading off of them. He RUINED Thanksgiving this year for my whole family, and I still have not forgiven him. What millennium said is right though. It's up to your parents to lay down the law. Have you talked to them? Obviously stress after surgery is something you should avoid, and your parents must get that as well. If they don't do something about your brother to give you a better environment, perhaps there's a friends house you could stay at.