I see the Sannin taking it extremely high difficulty, Orochimaru is probably going to be the sole survivor if we're thinking logically. Itachi can't be reckless and spam his MS techniques because if they fail, his stamina takes a deep toll.
Let's do it like this, Katsuyu is summoned, and she goes into her gel state, this way Orochimaru doesn't need to worry about his regeneration being costly; and thus summons his snakes all throughout the battlefield. You may be wondering how no name snakes are going to affect the battle in the sightest. Orochimaru in the forest of death, has shown the ability to emerge from his summons, similar to how he emerges from his mouth; albeit he comes out of the side of their body. This'll allow him to scatter through the area to gain different angles to help.
I'll stick Jiraiya on the main offensive; his elemental combinations with Bunta should be overwhelming enough for Itachi to resort to Susano'o, this is where Tsunade comes in. While Itachi is defending from blazing heat, she'll attempt to sneak in from the back and shatter the back of the avatar; Orochimaru quickly spits out the Kusangi and impales Itachi through the chest.
Honestly, this is the only way I see them winning.