Am I wrong for feeling this way?

It sounds like your family's financial situation is very stable, so I don't think it would be a big problem to your dad if you did not pay rent anymore. You could also consider cutting it in half and not completely, so that you still do something for them, living in their house(?). 250$ extra is already a lot added to your 600$. (Maybe I misunderstood that) Comparing oneself to another person is never really a wise thing to do, because it can cause dissatisfaction. There are always people who suffer more or live better, even when it's family. And most of the time girls have it easier, and parents expect their sons to be more independent. She's seems to be the youngest in your family too.