Another Percy Jackson and the Olympians Group... discussion

I'm not sure who should play Nico, I mean, first he's a ten year old boy with an obsession with a card game, and now...now he's just, I don't know how to describe him now... And Bianca, well, she's a hard one for me too, 'cause I've akways imagined the Di'Angelos as really pale with obsidian eyes and jet black hair, but they're described differently...Tell me who yo think should play them so my mind doesn't explode from thinking too much. AAAAH!!!