I think the main problem is the anatomy, especially the legs. It's partly because of the style you want to draw, of course, but the heads are too large in comparison to the bodies, even for a "manga style". The hips are too small and the legs too short. The faces look alright, and clothes too. Their "tubes" are a little wobbly, though. If you paint in Photoshop, try learning the "path" tool (P) to make vector paths of long and soft shapes like these. It's a bit tricky, but can pay off.
