Tsunade is probably stone dead, since katsuyu or whatever the snails name was were helping the kages survive and after that helping here, but in this case, in the middle of everything sakura decides to summon katsuyu ^^ what a bummer....
This isn't Gamabunta. Naruto summoned Gamakichi, who is the son of Gamabunta. So, probably, Sakura's slug is Katsuyu's daughter and Sasuke's snake is Manda's son, or Manda II.Gamabunta aint the son of Jirayas summon ^^ altho we've never seen Jiraya summon his best one, just the one that is perfect for the moment. So it's hard to tell, but since Jiraya had such control of which one he wanted to summon i guess Gamabunta was his ^^
And how do you guys know it's not Katsuya?