Board Thread:Naruto Discussions/@comment-25464204-20140925215818/@comment-5407586-20141001055431

It wasn't stated that the transmigrants are related to each other, only that they're all descendants of Asura or Indra. Sasuke doesn't seem to be Madara's direct descendant, while Obito stated to be one. Naruto's a transmigrant of Asura because he's his descendant through the Uzumaki clan which is distantly related to the Senju clan. Not to mention Kushina was born in Uzushiogakure, while Mito lived in Konohagakure.