Depends, if the duo can engage Sidous in lightsaber combat they could probably take him, but if he manages to launch a Force Storm at them they're screwed.
In saber combat, Sidious in DE absolutely destroys them. He doesn't even need a force storm, one of the several million other dark side attacks will suffice
I dont think Sidious could take these two in a lightsaber fight. After all he lost to Luke in a saber duel and Mace is a much better saber duelist than DE luke. Dooku also possibly.
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When the darkness comes, keep an eye on the light no matter how far away it seems.
DE Luke is able to deflect walkers with a saber alone and fight faster than the eye can see, tearing apart one end of the room to the other in seconds and channel the entirety of the lightside?
Luke by DE is easily better than ANY PT Jedi. Anyone able to contend whatsoever with Palpatine in his younger body with all his powers?
And Palpatine could simply raise his hands and make fists...fight over
You don't see Palpatine in a sixteen year old body post twenty something years from ROTJ with all the powers flowing through him in the darkside, do you?
a) He's superior to either Dooku or Mace in a lightsaber fight by the time of Dark Empire. Perhaps not both, but easily either one of them.
b) He isn't restricted to just lightsaber fighting. His Force powers are leagues above either one of them. Force Storms can be controlled in size, and his Force Lightning mortally wounded two strong Jedi in short bursts.