Do what I did. Challenge them each one on one. Beat the hell out of them. Just make sure you do it in a way that everyone understands it's settling differences, not just senseless violence.
I beat the shit out of Tara's brothers in one of those "get it all out here and now" fights. And ever since the three of us got along great.
Yep. It's the whole dominance thing. Brothers always feel the need to assert that they are dominant over anyone interacting with their family, but removing that preconception in a way that shows you aren't just showing them who's boss, but that you understand where they come from and aren't just going to back down, understandings come a lot easier than if you just wreck them or let them continue to think that way.