Hiruzen is the most experienced/wisest of the four (he's the oldest), Hashirama was the man with the original vision and i don't see Tobirama/Minato competing with these two hmm
the situation is not possible/won't happen but, i'l answer within the scenario you created.
the leader would be Hashirama for many reasons :
- he has the original vision/the man who made the whole thing happen.
- Hiruzen would respect that looking at how he respected/followed Hashirama's lead in the fight against the Juubi/Madara/Obito, as a result he would be an advisor.
- Tobirama would also accept his brother as his leader and would probably take over the Anbu (like Danzo) as well as being an advisor.
- Minato would never go against the will of the previous Hokage's especially the third's, so he'l play along and of course a legendary Shinobi with his skills will be a great asset to the village.
overall i don't see them fighting each other.