User blog comment:Lauren Darkmore/The RWBY AMA on Monty's twitter/@comment-10390252-20131111000031

That one about Ruby and Yang...?

Okay, so maybe they're cousins? Or has Monty been trolling us all this time and they're sisters-sisters after all. After all, there isn't automatically going to be a naming convention on Remnant of passing on family surnames. It is possible that you give a child that you think suits them, not one that automatically identifies their family.

If that second idea is right, it has suddenly become way harder to work out who is related to who in this show!