problem is...one of the first databooks (just as much fact as manga itself) stated that the sharingan mutated from the byakugan. This means the uchiha (only known sharigan users except for transplants) were most likely another lesser family of the clan who got all emo as the uchiah are known to do and ran off and ofrmed their own clan and over generations evolved their own eye. Following this, the older brother was most likely a hyuga not an uchiha since it never specifically says older brother = uchiha younger broter = senju. So based on what that databook says, the 2 original clans are senju and hyuga and the uchiha and uzumaki are watered down "cousin" clans. The reason the hyuga took a back seat is because when you recall back to the first series in the exams, for a good portion kishi wrote the manga in such a way that not only could sasuke be a bad guy, but neji could have as well for different reasons. On the hand of sasuke, you have the emo kid from the high ranking clan who is the sole survivor except his brother who slaughtered their family, leaving sasuke wanting revenge. On the other hand you have neji who felt himself above everyone (and tbh at the time he practically was) but we also find out later (and this could have been his tipping point to becoming the villain) that he is actually of the lesser family and wishes revenge and death upon the main family and possibly the whole village because the higher ups would have known of this and allowed them to be slaves to the main family since the clans creation dozens or more generations in the past. Both had ocular jutsu specific to their clan that none could replicate, and both had specific motives for potentially becoming the villain of the series, but people responded to sasuke better so kishi solidified him as the villain. Think about it, the sharingan and rinnegan are so hyped its not funny but the ONLY other ocular jutsu that no one but a member of that clan can use was left at "you can see chakra paths". Neither had been really setup until after the exams, the only details had been one can see chakra paths, the other can see movement so fast they can practically learn any non specialized jutsu instantly...nothing more, so it was obvious kishi didnt decide where to go. BUT since he wrote in a databook the byakugan came first and sharingan mutated later, we can know that (unless the uchiha picked up the sharingan waaaaaaaaaaay after its clans creation) the hyuga came first and being the only ones with ocular jutsu, the byakugan came first which must have been the less potent version of the older brothers eyes, assuming that both brothers DID create the major two clans and the clans didnt just spring up generations after. Because when you think, the whole uchiha senju rivalry, everything came into play AFTER the exams, AFTER kishi decided to make sasuke the bad guy, although he made that databook before that point.