Well, first of all, I think they need to be simplified. You're trying to cram too many details into your tiny figures and that makes it more difficult to tell things apart. You need to separate them from the background a lot more. Changing the color of the blocks or giving them an outline might work. Also, I think the colors you're using are too saturated.
Something more like this, maybe?
I think there's also something wrong with how their hands line up and length of their arms, but I'll leave that to someone who actually knows how to draw isometric people.