Board Thread:Speculation House/@comment-27151765-20151102160804/@comment-26397825-20151103003137

Monty himself says they are half sisters though, which contradicts your theories. Also, in our world it is not uncommon nowadays for women to keep their maiden names even after marriage, and they choose whether the newborn baby has the mother's name or the fathers name. It's not too big of a stretch to believe that's what went on here.

That being said, the marriage status of Raven and Taiyang and Summer and Taiyang is still up in the air, as we've never had direct confirmation on those things, but the fact that Ruby is Taiyang's biological daughter is not simply because we have confirmation Yang is Raven and Taiyang's daughter, and Monty himself said that Ruby and Yang are blood related half sisters. That means Taiyang has to be Ruby's biological father.