So, I've been thinking. If we were to continue the PJO movies as is (which I am thoroughly against), I have an idea on who should play some characters.

Rachel:

This is Holland Roden. She played Lydia Martin in Teen Wolf.

Nico:

Ian Nelson, also Teen Wolf

Bianca:

Crystal Reed. I don't know what she's in now but she was in Teen Wolf seasons 1-3

OK that's what I got.