My color vision isn't really good enough to give you any helpful advice on the skin shaders, although I think the lighting looks a little off. The skin looks sufficiently different from the background that they don't seem to match up.

The composition is a little confusing, too. I see what you're doing with the plants, but the grass doesn't look natural, because it's out of proportion with the plant life in the background, and because it doesn't seem attached to the ground. The background seems very natural, and I can get why the characters are there, but the grass in front seems out of place.

The background looks like it's a photo, and was taken at an angle that doesn't fully show the ground. I think if you move the characters a little bit so that their feet don't show, it'll remove some of the tell-tale blending with the background where the feet are.

If you do another take on this picture, I'd love to see more.