Not going to get heavily into it, but I will point out somethings, and why I think the Sand siblings are completely underrated here. First off I didn't know Oro was allowed to have Edo, with that it's pretty much over. The sannins win, without Edo the battle is much more even.
You're forgetting one thing here, they are in the desert, Jiraiya is not making a swamp as big as a desert. You also have to take into account that making a boiling swamp will make it harder for his teammates and summons to fight in. While Gaara can simply bring Kankuro and Temari in the air with him. Rasengan is out of the question for Gaara, maybe Kankuro and Temari if he can get that close. Also, summons in general aren't a wise choice in this battle because of Temari. She would slice them in half like a hot knife trough butter. Someone who can level an entire forest with a swing of her fan shouldn't be underestimated.
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Neither Summon, nor Tsunade is surviving that, and don't give the whole limb regenerating thing. Tsunade is not going to regenerate her head. Jiraiya on the other hand can put up his barrier, and Orochimaru can use the Rashomon Gates. While Oro uses the Gates he can't move because he has to wait for the wind to stop, meanwhile Gaara puts up a pyramid and seals him. See what I mean? There's many ways this can go, not just only Sannin this and Sannin that. As for Sage Mode, if Jiraiya can get into it it's going to be a long night, but it's going to be extremely hard to get into Sage Mode, even harder than it was against Pain. There is sand everywhere, no matter where Jiraiya goes he can be killed instantly if he makes a mistake.
I'm not saying the Sand siblings would pwn or win 24/7, but they stand a much better chance than you're giving them credit for. I say without Edo Tensei this is 50/50. Oh, and Tsunade is no where near immortal, she's the easiest kill in this fight. Whatever you're smokin' put it down.