This is pretty good! You've definitely caught the personality of the characters. Good work!
There are a few bits that could be tidied up. Some line work, the anatomy of a hand, etc. For example:
Changes:
Left edge of hair, reworking to allow a smooth curve rather than a corner.
Arm on the left: sharpening the sleeve, thinning out the line between sleeve and shirt, giving the arm some room.
Hand: resizing fingers and thumb. Changing the line underneath to look like shirt in the background rather than a thin pole holding up the hand.
Ponytail: sharpening the point.
Once you look with the right kind of eyes you'll see more little details scattered around that you can sharpen, round off or otherwise improve. Each one is a little puzzle.
If I get some time later I'll look at the hair and beards of some other characters. Looks like an interesting challenge, and you've done well with the space available. Some of it is really very good! I wonder if there's a better way to do your dithering, but I won't know until I have a go.
