Hello there.
My biggest concern is that they all look related

This is mainly because their facial-traits are the same, the nose and the jaw. I see that you have shaped the jaw smaller of some, but I think you can shape it even more. Also the nose should be modified on some, otherwise I think you did a good job considering the small workstation, which leads to the lip question; well it wasn't as easy as I though. I think the lips look good.
Oh and another thing! You could add some facialhair to differ their looks, also maybe some life experiences? (scars, tattoos) and headgear, like a bandana or a cap. Theese are just ideas!


That's a half-orc you're looking at. :- )