
I absolutely agree with K'nahli on just how taboo OP's setup is. Unrequited love with her twin brother that she rarely, if ever, brings up? It's not as if she's being forced into an incestuous relationship by her brother/father/uncle, etc. It's not exactly common, no, but as far as 'mature themes' go it's pretty tame.
OP, you seem to have a good head on your shoulders and have a pretty good idea on how to handle this. Like others said, so long as you don't turn it into a Japanese Light Novel, the few people that do find out about it ICly/OOCly should have no trouble rolling with it, and those that do... well, screw 'em. You've already seem to have given it a lot of thought in how you are going to handle/present it and what impacts it will have on your character, which sounds golden to me. Godspeed.
OP, you seem to have a good head on your shoulders and have a pretty good idea on how to handle this. Like others said, so long as you don't turn it into a Japanese Light Novel, the few people that do find out about it ICly/OOCly should have no trouble rolling with it, and those that do... well, screw 'em. You've already seem to have given it a lot of thought in how you are going to handle/present it and what impacts it will have on your character, which sounds golden to me. Godspeed.