Oh my gosh! This is lovely! The outfit Twilight has on looks gorgeous! The hands look a little iffy, especially Rarity's, but I'm assuming they'll be fixed later on. Some reference will be useful if you need them ^^
Also, Twilights area above the privates looks a little.... big? Like, if you look here:
[link] it's sunk in and bit more, but on your piece it's a little too round, I guess. I hope I'm making sense here x'D