It is NOT a summon, It's a jutsu to stop kurama, he previously summoned 6-8 arms and it didn't work, so this time is a 1000 arms.
It is NOT only hashirama who can stop a tailed beast, The first raikage also did so 1v1...
it is NOT same Sage mode as jiraiya, yondaime hokage or naruto's. My opinion is that this sage mode is like Goku's genkidama. He absorbs chakra from all living things/plants around him.
Hashirama's wife didn't participate in the battle, she is summoned once he has beaten madara and has kurama out of Madara's Genjutsu.
The only Summon is the Quintuple Rashōmon. This summoning technique is also used by Orochimaru when fighting against naruto in tailed beast mode before "Shippuden" He summoned a "triple" and ran out of chakra.
I do agree with some people that this has gotten out of control, if he includes hashirama and tobirama in the fight against madara. The most possible thing is that hashirama breaks them from Orochimaru's control and they will join the fight against Madara. Leaving Sasuke behind still undecided. I dont see the point of going thru all this trouble if he is not going to convince Sasuke, when could just beat them right there easily. This would mean that would never be a naruto vs sasuke fight. I would like to see Naruto die and Sasuke turn hokage after beating madara, that would be an evil twist. Naruto has been saying too much that he will bourdain everything on his shoulders and that not a friend will die, he might sacrifice for Sasuke making him carry his "will of fire"