True, any one of them could...but it kind of defeats the purpose. If Bane did it, for example, then he risks getting killed by either of them at any point, b/c he can't watch them both all the time...and try to keep them from knowing about each other. It obviously takes a real commitment to the plan.
With 1000 years between Bane and Anakin, there is potential for all sorts of "rule" breaking by potential Sith. But I think it's safe to assume by the time Palps shows up they generally kept it to 2 all along the way.
With 1000 years between Bane and Anakin, there is potential for all sorts of "rule" breaking by potential Sith. But I think it's safe to assume by the time Palps shows up they generally kept it to 2 all along the way.