So we know that the sage of six paths had a brother. He told Naruto that. So the question is who is the brother? He could possibly be the predecessor to the Uzumaki clan. It makes sense if you think about it. We already know that the Senju clan and the Uzumaki clan are distant relatives. Kushina Uzumaki told us that. We know the Senju and Uchiha are descended from the Sage of Six Paths. So the Uzumaki clan could be descendants of his brother. In that case Naruto and Sasuke are cousins. 