Gai and Minato should be able to win.
-Ay is a massive hindrance in this fight. I mean, 7th Gate Gai or Minato would beat him easily, but even ignoring that little factoid, him being on the battlefield will make Bee reluctant to use a bijuu dama, just like he was when he fought Kisame whilst alongside Ponta and the Enka geezer.
-Minato was able to spread kunai nigh instantly around a being with a radius as large as the juubi. He should have no difficulty in spreading out his markings quickly enough.
-This brings me to the next point. Minato being able to do that means that any bijuudama Bee fires is casually redirected with the S/T barrier, and if he has any markings in the vicinity of Bee, he would cause Bee to damage himself. Bee survived the full force of a bijuu dama, yes, but he was also knocked out of Bijuu mode and left in horrible shape. This happening will let him be easy pickings for either Gai or Minato. Minato could also teleport them behind the Hachibi. Overall, a bijuudama is not taking out Gai/Minato.
- If Bee decides to not use the bijuudama, he is left as an easier target for Gai and Minato. The challenge in this fight is actually putting Bee down. But Minato has a wide array of toad summons to restrain the Hachibi, and I think he can summon Fukasaku/Shima, who can cut through Animal Path Rinnegan summonings with their tongue. There's also Goemen, which when used with Gamabunta's oil, would be much stronger than Jiraiya's, would lead to some damage. This all sounds like minor or trivial damage, but over time, and with no way of hurting the duo, the damage will pile up on Bee. This is not taking into account Gai's Hirudora, and if used consecutively in weaker areas, together with Minato's own attacks, they should be able to put Bee down. Overall, Gai and Minato win mid to high diff.