Take this with a grain of salt. I don't think there are enough good critiques given in the fandom, so I'm trying to do my part.
First: I can tell that you're using construction lines to get the general shape of your characters. This is good. Keep doing this. You just need some work on proportions.
Brandice needs more mass between her boobs and her hips. With the structure she has, she doesn't have the core muscles necessary to hold her torso up.
Trevor has more of a feminine shape. Remember that males in general have hips that are narrower and taller than females, who have wide hips. Trevor has awesome girl hips, unfortunately he's supposed to be male. In addition, his pecs are taking up way too much room in his torso - your pecs end about where your sternum (breastbone) stops)
In general, both figures have necks that aren't wide enough to support their heads and their arms are too short - resting arms that are just hanging down should have their elbows about in line with the bottom of the ribcage.
As for face construction, it's highly anime/manga derived. On the descriptions of each of those faces that you drew, you stated what species each character was. I'm sure glad you stated that, because there was no way I could tell otherwise.
I'd recommend digging up some references and practicing sketching human proportions. You can find Loomis' books here: http://placidchaos.com/AM/index.php/2006/02/21/andrew_loomis
He's the authority when it comes to learning how to draw figures.
Hope this helped.