Actually, I recognized the bat character before I saw you mention it. She reads pretty fine, good work there!
As for color choices, I really don't know! The ones you have right now give everything a vaguely mature look, like faded renaissance paintings. This works well with the semi-realistic style you're rolling with.
The dithering in some places might need some touch ups but for the most part it also adds to that and gives the skin some texture, it's very easy to imagine these scaled up into non-pixel portraits.
I think the biggest problem area is the lines in some places, right now everything here has a slight jaggy look that detracts from the end result a bit. Do another pass over your various curves and see if you can tweak the curves to be more smooth. To point out some of the examples I mean, the rightmost elf girl's hair needs some very slight tweaking along the outline and so does the far-right girl's curly coat fluff!