Hello! I'll be focusing my feedback on anatomy, though there is a bit of perspective involved, too. The main thing I noticed was that for both of the characters, their hair did not follow the orientation of their heads. For the girl in the back, I marked the center line of her face, which is at a very sharp angle. I then drew a sphere to represent her skull, but that sphere's position is based on the orientation of her hair. As you can see, the sphere and the center line don't line up properly. The actual shape of her head is not aligned with her features, and the parting point of her hair is very far from the center line. Given her hairstyle, her parting point should be synced with the center line. So I drew a Loomis head to show how her hair should be angled to align with her face. For the girl in front, once again the sphere of her cranium is not lining up with her features, and her hair is not following the perspective of her face. Her features are squashed and stretched, and they're angled to be more forward-facing, while her jaw and hair are closer to being in profile view. Over-the-shoulder is a very hard angle to draw, so good on you for trying something this complicated. How I went about fixing it was by drawing a Loomis head at a 3/4 angle, and making sure that the hair followed the angle of the center line. The center line of her face curves along the top of her skull to the back of her cranium, so I had the lines of her hair flow in that same direction. I also angled her jaw up because we're looking down at her in this image. Beyond that, one obvious issue with your perspective is the brickwork. The purple lines show that, largely, you are converging properly to a vanishing point. The pipe in the background is perhaps angled a little too low, but otherwise you've got those lines going in the correct direction. However, the brickwork on the closest wall throws off the perspective. Those foreground bricks should be going in the same direction as the bricks in the background. I marked with a red line where those foreground bricks are actually angled. If you have the foreground bricks all angled toward the vanishing point that the purple lines are pointing toward, it will dramatically improve the perspective and the overall believability of the scene. I hope this is helpful!
