User blog comment:Holly Winter19/Reincarnated Hinata?/@comment-32296239-20190817201627/@comment-32296239-20190818005823

It is not easy to explain how it works since we have the Edo Tensei and reincarnation contradiction:

The Edo Tensei binds the soul of a deceased person to a living vessel, restoring them as they were when they were alive in order to do their summoner's bidding.

Now, as you know, it was said that Hashirama and Naruto are both reincarnations of Ashura so the three of them could never been physically together in the same place. The fact that they revived Hashirama being Naruto alive could not be posible in first place.

On the other hand, the souls of Minato Namikaze and Hiruzen Sarutobi were sealed by the Shinigami in its belly. So we must asume the Edo Tensei can break that seal, however this there is not logic explanation for it to be able to duplicate a soul.

My guess: Kishi didn't think about it at all.