Love the concept of the battle, first off.
While Maul, Dooku, and Vader (I assume you mean in the suit) are exemplary duelists, Darth Sidious is in a class above theirs. Maul is an aggressive Form VII specialist, certainly capable of keeping up with his master for a few blows. However, Sidious has not only beaten both he and his younger brother, without great effort, but his fluid and rapid style of combat is too quick. Dooku, the finest Form II specialist alive during the Clone Wars can certainly hold his own. Sidious claimed Dooku could learn little of the lightsaber from him. As the most technical duelist, he could probably last longer individually and be crucial in the fight. Darth Vader on the other hand is powerful but slower than Sidious. All in all, a three on one duel could swing either way. Without force powers being used, I give it an even 5/10 either way. Reason being is it depends greatly on how well the Apprentices can mesh with each other. The power driven styles of Maul and Vader and technical precision of Dooku relies on their positioning throught the battle (something Dooku is a master of). If they can force Sidious from two different angles, it would draw his attention to keep up allowing Dooku to get close to try to deliver a fatal stroke. I can see it going the other way because Sidious is a master of Dun Möch and if he can place enough doubt in one of them, he can cleave the errant apprentice from the herd (Vader has been proven to be susceptible to this technique and probably has the most trouble managing his emotions). From this point, he can, after a tough fight prove victorious.
Round two is much the same, just at a higher level.
Round three slants it directly in his favor. Force lightning < Vader. His mastery of the force, including his powerful ability of foresight can help him crap all over them. Vader with his full body could probably put up a night at full power. Dooku is probably the most technically proficient in the Force (appropriately). Maul is stron in the Force but he is like a torch burning next to the inferno that is Sidious. Perhaps 8/10 Sidious.
Round four works even more in favor of Sidious. Dude can generate a storm out of the Force (been a while since I read the materials). 10/10 Sidious.
Can't say for bonus. I'd like to see them take on Darth Bane though.