Why Madara's bother, and if he somehow obtains Senju D.N.A. e can get it. If he fight Madara, or Tobi and gets a splash of blood on him he'll receive some Senju D.N.A. right then and there. that's how Madara got it during his fight with Hashirama he must of somehow got ahold of some of his D.N.A. that's how he got the rinnegan at the end of there fight.He won't get rinnegan, only person who can naturally get it that we know of is SO6P, Madara and Madara's bro.