Hyuuga and Uchiha clan family roots? The Uchiha clan is descended from the Hyuuga, right? So then why is the Hyuuga clan not seen during the founding of the Konoha Village? How did the Uchiha awaken Sharingan, when originally they had Byakugan? How did they come into changing their name? Would an Uchiha be able to awaken Byakugan? On that note, what would happen if a person were to obtain byakugan, eternal mangekyou sharingan, and rinnegan?

EDIT (4/2/14):
So now Kaguya is shown to have Byakugan. It is evidence that Uchiha, Senju, and Hyuuga are indeed related. But how does the Hyuuga then come about?
The Uchiha are not a descendant clan of the Hyuuga. That was speculated by Kakashi in the very early stages of the series.

Much more information was revealed afterwards (SPOILER! Hover to view):


   Both the Uchiha and the Senju (The clan of the First Hokage) are descendants of the Sage of Six Paths, who created ninjutsu and had the powers of a god.


Also


   A Rinnegan is the next stage of evolution after the Mangekyo Sharingan, so you can't really use them both at once on the same eye. The Byakugan has nothing to do with it and is a completely separate technique.