Ah... I remember this image, with different characters of course. Rolf and Amy from the Compendium, wasn't it, Xan? Still, I don't blame you for using images there, it's an excellent source of reference.
As far as constructive criticism goes, Chaz's face is a little too manly, of you know what I mean. He has a very childish, boyish look about him, and the ears are a little too high up on the head. You might want to move it down by a little next time you draw. The ears are a bit small as well, and Shorty could use with a little more shading on his armour.
Add more variants of grey. There's currently too much white in the shading.
No complaints with Kyra, though. Love her expression. You captured it very well. Though you might want to add a little more white or lighter yellow to her gold collar. It will have a more metallic effect.
So yeah, that's my own little opinion. But you are improving very quickly.