You're forgetting that the lightsource in SRB2 sprites is mainly supposed to come from above, yet the shading in Charmy and Vector's front sprites hint that they are coming the top right. You should try to make Vector's head overshadow a bit of the middle of his chest and that's about it, really. As for Mighty... he looks crosseyed, as his pupils are too close to each other. Not only that, but it's too evident that all you did was take Sonic, shove a shell in him, and give him grey soles. You could have at least tried to fix up his arms to not be posed exactly like Sonic, and fixed his shoe shape, because they are not supposed to be as pointy. What bothers me the most is that you just mirrored the shell and didn't even bother to fix the ridiculously wide shape, nor the brightening upon his head:
Also, I really appreciate that someone is trying to make use of the Chaotix sprites I made, but... you are using it in the wrong way. It's way too evident that all you did was just rearrange parts from the original sprites just to save you from doing all of the body parts from scratch, but bad news for you, though... it looks heavily unnatural. Vector's headphones are sticking too much out of his head, his hands are just copy pasted from the diagonal sprite despite this being a different angle, and his feet are not even angled forward (why would his stand with his feet like that?).
So if you want to get better at spriting, you better start getting used to spriting a character's other angles and animations from scratch, and actually look up for character reference to make sure they don't look out of model.