At the 5 kages summit,Tobi did told a story of Rikudou Sennin and about the 2 brothers.The older brother was given the ocular power but,short life force.The young brother was given a powerful chakra and long life force.Tobi claims that the Uchiha clan was the one from the older brother and Senju clan was the one from the young brother.I think,Tobi might be wrong about the Senju clan is from the young brother.In the story,the clan that have powerful chakra and long life force is Uzumaki Clan.Uzumaki Kushina has proved it when the kyuubi was taken from her.Kushina should be died after the kyuubi was taken from her.But,because of the clan long life force,she still alive after the kyuubi leave her body.Even Naruto has a powerful chakra.The frog that teaches Jiraiya claims that,in order to be a sennin,someone needs strong chakra and a guts not to give up.Jiraiya didn't perfectly in the sennin mode because his chakra wasn't strong enough.Naruto prove it that his chakra was strong enough to gain the sennin mode.

So,I think,Tobi might be wrong about the Senju clan was from the young brother at the 1st time.Tobi only drives by the evidence that the only clan who can keep up with uchiha is senju clan,but it didn't prove that the senju was from the young brother.Senju is just a distant relatif of Uzumaki clan.The story about the young brother has a powerful chakra and long life force most likely same as Uzumaki clan story.Maybe,Tobi attacking konoha 16 years ago because he wanted to prove his theory about the young brother story,which is he want to know whether Uzumaki Kushina will died after he taken the kyuubi from her.As a result,Kushina didn't died.So,his theory about the Uzumaki was from the young brother story is absolutely right.Tobi told the story that the Senju clan was from the young brother story is just a lie to cover up Madara's mistakes.The real story behind Madara and Hashirama battle is I think Madara want to gain Uzumaki Mito DNA.But,he got Hashirama DNA instead.Edo Tensei Madara have said that,he activated the rinnegan a short second before he died.So,whose the person that going to make an experiments on Hashirama DNA,since we know that Madara is death?I'm absolutely sure that person is Tobi.Whoever Tobi is,Madara already planned everything with him,except,Madara didn't told Tobi an info about the Uzumaki clan.I bet,the left side of Tobi body that have rinnegan is an Uzumaki DNA.

But still,that's just my thoughts.There must be wrong info that I put in it.I'm sorry if anything that I said make you guys angry.We can share our own opinion.But,I know,my thought sounds ridiculous..haha..