I don't have proof really but Simple logic really the sosp is said to be the origin of all ninjutsu the sage split his two bllodline senju and uchiha(not uchiha and uzumaki) so todays ninjas consist of two bloodlines senju and uchiha the uchiha inter married to preserve their bloodline why the senjus didn't so the senju clan was further broken down to other smaller clans and uzumaki is just one of those clans uzumaki are a close relative to the pure senju that's why they have huge chakra reserves am sure kishi will break it down soon and it will be very similar to the I have said it
Doubtful.
The Younger Son & Elder Son are the Ancestors, nowhere does it imply that they're the actual Clan Heads.
As Tobi stated, their descendants eventually became the Uchiha & Senju.
You do know that the Uchiha are distant blood relatives of the Senju, does that make the Uchiha apart of the Senju?
