They are pretty much perfect for the most part, but I made an edit to show a few things.
1) The woman and man -
I suggest using less colors, as shown in my edit. But if you still want to use more colors, that is fine too. But I would make more distinction between the colors. For example, the color for the skin should use 3 easily distinguished colors. As they are right now, they look too much the same and dont stand out enough and make it look slightly blurry. I hope that makes sense.
2) The monster -
My edit just shows a slightly different way of shading. Not much really.
3) Ghost -
The highlighting looked like pixel banding(I think that is the correct term Im looking for) so my edit tries to fix that. I also showed it using one more color.
Excellent characters, by the way!