From what I understand, falling to the dark side does not necessarily make you a Sith. A Sith is a dark side force user who accepts certain teachings, observes certain rituals, as well as aligning themselves to a certain historical legacy. Dark jedi lack the cultural background to be considered Sith. In a later era, after the Rule Of Two is instituted, Sith would often use Dark Jedi as pawns. A common way for a Sith Master to gain the loyalty of a Dark Jedi is stringing them along with promises of accepting them as their Apprentice.

As I understand it, under the legacy system, lore says that your main and all your alts will be related in some way. Like Luke Skywalker was just Anakin Skywalker's alt.. I guess. So your alts are you main's son/daughter/brother/sister/family friend/ 3rd cousin twice removed for unnessessary roughness. So how are you planning on justifying those ties? When my Bount hunter discovered his son was Force sensitive he did not wish to subject him to the sith academy, so he sent him to the Republic. To be REALLY sure no-one would figure out who he was, my Bounty Hunter gouged out his eyes to disguise him as a miriluka! The fact that the child kept his orginal family name is so cause for concern as Luke Skywalker successfully hid from Darth Vader for years with Vader's brother's family on Vader's home planet without anyone catching on.