Yata Miror for shielding off both attacks Amaterasu on Kakuzo, Tsukuyomi + Totsuka Blade on Kisame.
Easy win for Itachi. Two Straight Forward Elemental Ninjutso users is easy.
Kisame and Kakuzu have the elemental advantage since they both have water style.
Kakuzu needs to be killed 5 times and if he is hit by amaterasu then he could just split bodies. Itachi can kill Kakuzu but he will then be too tired to go up against a chakra demon like Kisame.
If Kakuzu is hit by Amaterasu he can just split bodies.
Kisame could probably beat him on his own in my opinion.
Itachi Med difficulty.
Kisame could probably beat him on his own in my opinion.