Board Thread:Speculation House/@comment-68.186.83.101-20130601225528/@comment-4010415-20131007120357

Cyrus Arc wrote: It must be confirmed that Ruby and Yang are, in fact, sisters. They could have been greeting each other with affection (Like guys call each other bro) or they could even be half/foster sisters that don't share the same last name. "You see, my sister's starting there this year, and she's trying to become a Huntress, and I'm trying to become a Huntress cause I wanna help people. My parents always taught us to help others, so I thought, 'Hey, I might as well make a career out of it!'" - Ruby Rose, in the pilot episode.

Plus the fact that Yang said "Oh, I can't believe my baby sister is going to Beacon with me! This is the best day ever!"

So, they are sisters, but like Monty said, they're not blood-related.