Not happening. 6 paths wreck this duo. Itachi's strongest defense (V4 Susanoo w/ Yata) is busted open with CST, or he is simply outlasted until he can no longer hold it up (which he will be forced to do, in order to protect himself and Kisame from constant attacks). He won't be able to effectively use Amaterasu or Tsukuyomi against the Pains while he's also using one of his higher Susanoo forms. Bansho tenin may also be able to effectively yank Itachi out of Susanoo (the same way Gaara's sand yanked Madara out of Susanoo). Kisame's water dome is useless, as it gets popped with a Shinra Tensei; GSB can be blocked with Shinra Tensei or an animal summon, or absorbed by Preta. They also have no counter to CT. Kisame's merging-with-earth Doton is not high level enough to withstand the pressure of all the rocks that the CT core attracts, plus that Doton has only been shown to work on the earth, not a Chibaku tensei moon that's made out of thousands of boulders.