5 Kages win high difficulty.
Ei can counter all the advances of his father(3rd Raikage) with his superior speed, thereby stalling him and preventing him from blitzing the others. 3rd Raikage will not have his way with A idc what you people say.
Onoki can prevent Muu from decimating the Kages by countering all of Muu's Jinton attacks with that of his own. Also I believe Onoki's dust release has surpassed Mu's based off of his last attack against Madara that cleared the entire battlefield. Also he has giant Golems and weight manipulation.
Kabuto would not be able to handle Gaara, Mei, and Tsunade. For all the people talking about the sound Genjutsu.... Tsunade can reverse the effects of genjutsu just as she did for Kakashi when he got caught in Tsukyomi. Tsunade is(theoretically) immune to genjutsu as long as she knows it has been cast.
Also Gaara could put up a wall of sand to block the sound waves, even if he is caught it's no big deal because he can still manipulate his sand freely.
Mei would get freed by the others.