Hmm, maybe it's a bit of stretch, but judging by Obi-Wan performance against Grevious, i think Soresu users have a kind of advantage in a fight against Grevious. Add to the fact that Barriss is a able to mimic Makashi quite well and That Luminara is a Shien/Djem So practitioner so they really do have a great defense bolstered by a great offense.
And there's the fact that Luminara has done - for the most part - Quite well against Ventress and Barriss gave Anakin trouble as well. I think Luminara and Barriss could potentially take the victory. That's just my opinion though.
Well Barris showed herself as a pretty decent duelist, she obliterated Ahsoka and did pretty good against Anakin.
She was quite the prodigy of a Jedi, in terms of bladework and knowledge simply because she devoted her entire life to it, and was incredible studious.
Unduli's a decent telekinetic, and would be able to keep Grevious busy quite well.
I really dont think this would be hard for them.