Wow, lovely work so far!
The colors seem a bit muddy, there is lack of variation in hue and saturation. You could also give everyone slightly different skin colors, making some more pale than others or so! And as for the lighting, I am a bit uncertain. It seems as if light is coming from the right only, as shown by the shadows cast by the mountains. This would make the scene more dramatic however, there should be a stronger contrast and overall, more shadows among the characters (it is too light if that were the case). Not a light expert, but I do think it looks off in that sense. Composition wise, it looks a bit weird. Not necessarily because it is bad, but the back of three characters take up a one third of the painting, and I am uncertain of where I should look. The center is a cluster of complexity, which works badly because distance usually remove details from our eyes, besides, the composition kind of drives me more towards the characters backs than the center. The mountains could also be a bit more separated from the platform of where the characters stand, for right now, it seems almost as if they're in the same field.
Either way, lovely work! hopefully this was helpful. 
