Yeah technically speaking there all great. Good facial anatomy, good porportions and all that crap that you need. A good job on that. The style is even pretty attractive!
..But your right..you need variance. All your characters look very very similar. Many faces have the same shape, eyes and even hair looking through all your posts. Youv got all the key stuff down well but now youv got that, play with it abit. tweaking the rules a little helps with making different characters.
Theres umm..a thing I saved somewhere that would be perfect for you..umm
There you go, that should help you out with variance.