With Katsuya, Tsunade maybe has a chance, if she makes it scatter itself on various locations to heal tsunade. If Tsunade can make it to Hachibi in time to stop a full-on charged TBB, she takes this. Otherwise, Bee wins this fairly easily. In terms of Taijustu, in her immortal mode, Tsunade won't be effected to a greater degree by the sword stabs, she seems quite resilient for those. So base Bee, doesn't seem like a problem to me. The actual problem arises with the cloak. If she gets hit, she will suffer damage, which will inhibit her movements. Bringing Katsuya in to use her acid spits and a few handy portions to provide that extra healing ability to Tsunade will prove to be quite beneficial.
Once Bee goes full eight tails mode, Katsuya might - like I said might- prove to be a distraction. With Tsunade's strength, attacking and taking out a few tails of eight tails shouldn't be a problem whose chakra focus enhances her natural monstrous strength ten fold. It all depends upon how Bee will react. In base mode, Tsunade takes this high difference. In eight tails mode, if Hachibi or Bee don't fall to the distractions, they take it low-difference. If they do, then it depends how much Tsunade can damage 8 tails to make it revert back to Bee, and once it happens, Bee cannot transform back for a large period of time, as the transformation will sap all of his chakra, and he's be completely vulnerable to Tsunade's attacks. Here, the whole fight is debatable.