The one with the open mouth has their chin/tongue tangenting with the bottom of the image, looks like an accidental crop. Maybe move them up a bit so that their whole face fits and has some breathing room?
I think the necks blend into the chins a bit. Perhaps making the necks darker (fully in shadow) would help.
The character on the right seems to have a very large face / small head, I think they could use a bit more hair, in both the portrait and the sprite.