Theory for the Uzumaki Clan...

[Razen]

If i'm not wrong the next time they talk about sage of 6 paths they confirm the boys were his sons. Anyway they already sayd in the manga that uzumaki are blood related to the senju and they already gave clues about hyuuga nad uchiha being the same way.

 

[Hikari Uchiha Senju]

Some guess SO6P was from the Uzumaki clan himself which is why it's related to senju, and which is why he has the same sealing abilities as those of the uzumaki.

I guess he also had a Hyuuga parent (rinnengan had to develope from something)....This also makes sence,since its tought that sharingan is developed from byakugan...