Hebi Sasuke would only defeat Mei one on one and Amateratsu is the thing that ensures it. But his speed wouldn't be the saving grace you think it is before a kage level ninja. Certainly not on the tier of Madara. His techniques to that point aren't particularly that impressive with the exception of Amateratsu. At that point the strongest katon he used was a less impressive version of Katon: Ryūen Hōka no Jutsu which was batted away by an exhausted Tsunade.This is a tricky one. Hebi Sasuke can most definitely best Tsunade and Mei, no doubt, due to his speed and techniques. SM Naruto can most definitely pin point their directions if Mei decides to use hidden Mist. Sugetsu is great for keeping Onoki Busy, as all his attacks would be rendered useless on a guy who can just liquify his own body and move wherever he wants to. But since this is gokake versus Madara, it means there is no water source and he cannot combine with a large body of water to combine with, so that goes out of the window.
Gated Lee can also provide a great diversion for the kages. Hawk can be summoned to blow away the mist and Manda and Gamabuta are quite good summons as well, and would greatly tilt the odds in this team's favour. Without using Clones, Naruto can use FRS 6 to 7 times. Sasuke can carry Naruto on his hawk and aim for Onoki as well, together with his senbon. Too many combinations to use here. I don't think the Gokage take this, but this team is not wining either. I don't know what to say here. Too tricky.