Actually they were DIRECTLY related to the senju.. Their descendants became to be known as the Senju, and the older one's became to be known as the Uchiha. Uzumaki are relatives of the Senju clan because they break off from them.. but are still part of the SENJU linage.. Same isn't said for the Hyuuga though. And if they were related I'm pretty sure there would be some sort of a relationship between Hyuuga and Uchiha. And, its not said "Hyuuga ARE relatives to uchiha"..its say, "they say" . Big difference.. you can't compare them to Uzumaki and Senju.. where its said Uzumaki are distant blood relatives of the senju. And are from that same linage.
They were DIRECTLY RELATED, but they WEREN'T SENJU. The Senju might well be the purest bloodline, but it wasn't the only one. The same would apply to the Uchiha and Hyuuga. If anything the HYUUGA seem to be the purer bloodline, as EVERY Hyuuga awakens the Byakugan, and the same is not true of the Uchiha and THEIR doujutsu.
Obito, well so far stated a fact.. its not been proven wrong. And we have already seen its work.. aka the Rinnegan. Senju + Uchiha dna = God eye Rinnegan. Why mention the Uzumaki.. since they are just part of the senju linage..... in fact weaker then the Senju.And sure their can be many others.. but they would have to descend from the SENJU LINAGE. The sage had the rinnegan.. but the power of the sage was divided into 2. 1 with body and huge chakra levels... the other with the eye power.. Both combined unlocked the rinnegan. That illustration isn't backed up mate.

. So I can't say anything about it unless its cleared out and is shown as a person in the manga.
Obito was telling the truth, but he WASN'T telling ALL the truth. He didn't include the Uzumaki and may not have included, or even known about, other descendants of the Sage.
Here's a page demonstrating Obito being a liar:
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So even if he KNEW the Hyuuga, or others, were related to the Sage, he WOULDN'T SAY SO. It doesn't help him, and Obito only tells people things which end up to his benefit.
It says "they say UCHIHA CLAN'S origins lie with the Hyuuga clan".. it doesn't say that Hyuuga came from the Uchiha.. Makes no sense.. since we know.. Uchiha's origins lie with the senju clan.
The Uchiha come from the Sage, the Senju come from the Sage, the Uzumaki come from the Sage.
The Hyuuga could come from the Sage. They're VERY similar to the Uchiha in many respects, posess both hallmarks of the Older Son, and the Rinnegan, Sharingan and Byakugan are referred to as "The Three Great Doujutsu". There are no others.
So, what are you saying, the Rinnegan and Sharingan are related but the Byakugan popped up at random? As well as there being NO other case where an ocular Kekkei Genkai came into being?
But Byakugan is weak..... lmao. If its the original eye of the sharingan.. then it should atleast match the sharingan's power.. lol. But again that statement has been proved wrong.
So then the Byakugan could be descended from the Sharingan, and therefore weaker. It hasn't been proved wrong, the Hyuuga just haven't been at all prominent in Part 2, where this has been discussed.
They manifest whisker marks because of having the 9-tails..lol. Actually the first Mito was just a coincidence.. and then Kushina was brought in.. since the senju just... faded away. And then Naruto well was a special case..;p.
And they survived the Nine-Tails because they were "special". Now, what bloodlines do we know which are special, and are demonstrated to grant power over demons?
Enormous chakra AFTER they ate the 9-tails meat. ;]. Why do they have to be related to the Sage? Can't they just be strong on their own??
They SURVIVED eating Kyuubi meat, something ordinary people don't. Affinity for controlling demons/demonic energy is a trait common to those confirmed to be related to the Sage: Uchiha, Senju and Uzumaki.
Yea Juubi itself is the chakra around the earth.. so in that sense it makes perfect sense. I see what you meant now. I thought you were following the weird theory have they going on about the Sage of 6 paths nowadays. My bad mate .
It's fine.