This whole manga since part 1 is about Naruto and Sasuke's bond. There is no doubt Sasuke is Indra.
That said, with the Naruto/Hashi and Sasuke/Madara parallels, I would assume Hashi and Madara were Asura and Indra, but Sasuke and Madara are both alive currently at the same time
Madara is Hagaromo's brother reincarnated? Or he's just Madara
In fact how does reincarnation work in this manga if people can be Edo'd and resurrected? :| Maybe Naruto and Sasuke are the only ones...because their spirits have unfinished business that spun the whole world into war?