So the Hyuugas must be connected to Uchihas as Uzumaki were connected to Senju.
Probably a member of the Uchiha couldn't awake the sharinagan and awakened the byakugan instead. Then either he was banished and started his new clan or left on his own and decided to make the byakugan the symbol of his newly founded Hyuuga clan.
Most likely a Uzumaki who possessed some unique traits to himself also did something similar as he started his own clan.
The connection between Uchihas and Hyuugas was hardly elaborated and neither was the confirmed connection between Senju and Uzumaki elaborated either. Kishi left so many open roads possibly for future plot lines but grew tired with the manga and decided to ditch those plotlines just like he ditched the Kaguya resolution.
Hyugas not being Hamura's children is just stupid.
why make things more complicated than they need to be ? Just have the Hyuga be Hamura's children and call it a day. Not this stupid nonsense about some random descendant of Hagoromo getting a Byakugan out of thin air.
Would have made more sense just to have Uzumaki/Hyuga come through Hamura and uchiha/Senju through Hagoromo.
Even with a god damn movie, these people fail to explain where the Hyuga came from. Same goes for the uzumaki. It's pathetic how out of the four Sage clans, only one got actual depth and development. not even the Senju clan, the so called rivals, had any good development in terms of history, politics, and power.
As for unresolved plotlines, remember the Hagoromo clan ? Lol too funny