Battle of the Heroes intensifies
But seriously, I'll take a shot at this, but since Idk much about Legends, I'll be happy to be corrected.
This fight would be much closer if this was ANH Vader or ESB Vader, but ROTJ Vader? From what I understand, ROTJ Vader is when he was at his peak in power and had long surpassed his ROTS self and Obi-Wan was just below Anakin in power by then. Vader is already stronger here imo regardless of it being 2v1.
Also, Vader has prior knowledge and experience on his side. His former self and his former master? He knows them both like the back of his hand. I wouldn't be surprised if he tried coaxing Anakin to the dark side and or throwing him off balance by revealing Anakin's failure to save Padme or something. Vader would just toy with his former self's emotions, counter all of his tricks and skill thanks to prior knowledge and experience and simply outclass him with greater power. Obi-Wan being the master of Soresu would definitely help him last longer, but in the end, he falls as well. After his failure on Mustafar, Vader has undoubtedly replayed the battle time and time again to the point where he won't be making the same mistakes and would know how to take Obi down this time. Also, the second Vader busts out the force, it's GG. Obi was screwed by Dooku once he pulled out his own force moves so who's to say that Vader, being much stronger than both Dooku and Anakin, won't do the same?
This is all on top of the fact that Vader's suit serves as armor to the duo's attacks and makes him much more durable and physically stronger than them despite the fact he's slower.
Anakin and Obi-Wan are faster here, they have numbers on their side and their teamwork is remarkable, but Vader has more edges in prior knowledge and experience, greater power, greater physical stats and his sheer willpower after years of what he's been through make me believe he takes this. I can see Anakin and Obi-Wan putting up a good fight against him and getting hits there and there, but eventually Vader will win.
Therefore, I vote Vader. Again, I could be missing info or downplaying Anakin and Obi-Wan since I'm not very familiar with Legends so I am open to criticism, but this is what I think.