Okay, it seems you've answered what I said about sitting with them and talking about it, but have you asked why exactly they don't like you being a Brony? They're probably just freaked out by it because it's outside of the preset guidelines that society has set for all males. Tell them some of the great things that Bronies have done for charity. Convince them to watch an episode, perhaps. A GOOD episode. Dragonshy. Yea. Season 1, episode seven, Dragonshy. Show them that, and if they refuse, simply keep on being a Brony. Rebellion, motha buckas!
Seriously, though, over time I'm sure that even if they don't come to like it, they'll learn to live with it.
...Christ. That's the biggest text wall I've made in a LONG time.