IMvHO, it's all too cosy. You've created two compatible lovers, with only an external threat (evil sister) to lend the story tension, and no real inner conflict.
Just suppose...
Cross-Dressing-Singer-Boy is desparate to prevent the rest of the world from knowing His Secret, but too attracted to Depressed Bi-Girl to resist flirting with her.... and one thing leads to another.
Now either he has to woo her without revealing his true identity...or else she does know his true identity and has to woo him without making him feel blackmailed or stalked.
Or, perhaps, both of them are in denial about their sexual personae. She only ever acts sapphic in clubs where nobody knows her, and only by pretending she's not really doing it, and then not really in control. He is deeply ashamed of his cross dressing, but can't throw it off. When they collide, both are caught in their most shameful state, and each has the other at a disadvantage... but there's this attraction.