Senju and Uchiha are related because both are the descendants of the younger and the older son of the so6p respectively, however the uzumaki were said to be related to senju, but nothing else was said about them, about the sage eyes you are right and I agree with you, we have to wait until everything is unveiledtrue it is an assumption and a mistake on my part but it further proves my point, one thing we can say is that the uchiha and senju where rivals nothings says they were related, but one thing is certain the uzumaki are related to the senju it says nothing about been relatyed to the uchiha so how could the uzumaki who has no relation to the uchiha posses the eyes of the sage ? it has been said that the senju descended from the younger son of the sage who inherited the sages body,then how come along their lineage someone suddenly develops the sage eyes ? (transplant: it has even been said in the manga) if nagato was part uzumaki and uchiha it would have been stated, if he had senju dna it would have been stated, but it wasn't. This proves nagato is purely uzumaki until proven otherwise by the manga. nothing in the manga suggests he unlocked it himself whereas it has been hinted and stated that he gained it through transplant.