Very nice work here, if I may say so myself. A few points though:
Annabeth looks a bit odd from the angle you drew her at--correct, but strange nonetheless.
Reyna is very well drawn, but compared to the other three, she looks dull and uninteresting. You even drew her in a pose commonly used to draw her.
Piper and Hazel definitely look the best out of the foursome. I like Hazel's sparkles, but she uses a sword, not a dagger. Try to make it longer... About four feet.
Reyna, Annabeth, and Piper all look like freshmen/sophomores, and Hazel look 13 to 14-ish. The backgrounds are different from how you normally do them, which is cool. Overall, this 4-part piece is not your best, but still just as great.