Well, i let my entire family find out themselves. I just started leaving my pony stuff out in the open and not hiding it. When they finally noticed. I just told them what a brony was, showed them some statistics, showed them some videos, and some fan made music. And other then the lighthearted comment every one ina while, the dont mention it.
It was worth it because, i can be more open about it and ask for stuff i couldnt if they didnt know