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?