Talzin cannot hold off Sidious. Yoda can hold off ROTS Sidious...and indeed did so, but the resulting draw is in Sidious' favor.
Vitiate is the wild card here, how useful he is depends greatly on what amps are around and how much prep he has. If the answer is 'sufficient to perform at his usual level' then he can take Talzin, who is most certainly not an Emperor.
Talzin tanked Sidious and then Sidious and Dooku simultaneously in one of her weakest states (she died during the Jar Jar episodes). Maul then lent her his power but she reacted by just Force Pushing him.
Full strength Talzin was strong enough to take on Sidious toe-to-toe, no wonder Sidious was peeing his robes at the thought of the even more powerful Gethzerion.
Talzin is more than enough for facing Sidious or Vitiate.