i'm being alice for the breaking dawn release, so i can share some of my ideas with you! my suggestion for your outfit is to study up on the latest fashions, seeing as alice is always in style. go for something trendy, but a little vintage; modern, but with a sort of turn-of-the-century twist.
as for make-up, be subtle. because alice is a vampire, she has flawless skin and is already gorgeous. my guess is that she doesn't wear make-up most of the time. use some concealer and a light, sheer powder on your face, a touch of smoky eyeshadow and some mascara, a little color to your lips and that should be all you need. remember: you don't want it to be too obvious that you're wearing make-up.
i'm not as sure about the rosalie costume. i imagine rosalie would go for something a little more on the feminine side; a short, slinky dress or skirt, classic high-heels. feminine, but confident. her make-up would probably be the same as alice's, but she seems like the kind of person who would be a fan of bold red lipstick, so you can try that out if you want.
i hope this helped some. good luck! : )