Akatsuki takes this mid-diff at most.
Sasori, Kakuzu and Deidara are more than enough to keep the fodder-army occupied. Honestly, I think the Kages would command them to stay back anyways, since they would be a handicap for them. Gaara would be constantly forced to protect the fodders from large-scale ninjutsu.
Also, Itachis weak stamina isn’t really a factor here, since his role in a group fight wouldn’t be to engage the 50.000 shinobis, but to observe the battlefield with his sharingan, deliver killing-blows to the kages or to block critical strikes with his susanno, if necessary.
Even if the kages manage to kill one akatsuki-member (which I highly doubt), he/she would easily be revived by Pein. Tsunade surely is hard to kill but she will certainly bleed, which gives Hidan the opportunity to do his ritual. Even with intel the kages won’t be able to stop him performing it, if he’s hiding behind Deva, Preta, Itachi or Kisame (they render most of the kages attacks useless).