Well as to the True Sith, I never saw them as a species. I prefer to think of it as a dark essence from what Kreia said about there were dark places in the galaxy and Revan knew the power of such places and the power in making them. After all the Sith is nothing more than an ideal.
The two PCs a definite no because for one I wouldn't be able to keep track and two, well I doesn't seem right.
There I've said my two cents and am leaving now.