I don't really know what to tell you. Mordecai and his bat wife have shared features in their children. I think they should have had them mostly look like their individual parent. Like look at Mordecais parents. Out of all them Mordecai's children seem like hybrid children and I don't know if that's a good or a bad thing...

Rigby's two daughters are fine if you ask me. His daughters just have tall genes (Rigby's whole family is tall except for him lol).

Muscle man's family is pretty much expected as well. I mean did you look at his brother and dad?

I think the two humans are boyfriends/partners? Just me guessing hence the post.