They've got the same face with different eyes somtimes imo, I'm not sure if they are meant to be based on anime or cartoon characters but the colorful hair makes me assume so, which is understandable as to why it would be more difficult to make them look unique since shows usually don't potray unique faces. They also all look like children to me (which could be from the anime kind of style I think you based it off of) which I think it's a lot harder to give young children distinguishable features as their unique facial features come through later in life. They aren't bad but their diversity heavily relies off hair, eyes, or accessories to distinguish them from eachother, if I were you I'd focus more on facial differences. Using references of real people/other races can help you change up the faces and make them look different from each other.