How did Obito know?

[HENI]

Someone Obito knows Naruto and Sasuke are the reincarnations of Hagoromo's sons ..

Remember he said that to Naruto during the snowy day.. ?

 

[Yanks]

Madara told him about the older and younger brother?

 

[NarutoB]

He just saw the similarities, I guess.

 

[Sentinel of Light Style]

he didn't know, just figured they were very similar to Madara and Hashirama

 

[VongolaX]

Madara and Obito have the knowledge of everything.

Everything Madara knows, Obito himself knows as well.

Obito was urging for the Ashura and Idara fight to happen all over again.

Nagato and Itachi were just pawns in developing the characters to a certain state, before the rest takes off.

If Sasuke was synced to Gedo mazou by Obito, Sasuke would be on his level.