So just quick and dirty:
My main character is a light sided sith warrior. My plan for his legacy is to have him and his twin brother to be children of two jedi who fell in love and left the order to live peacefully far away from Jedi judgement. When the empire invaded they got caught up in the war and in order to escape they split up and each took a child.
The father and one child made it to the republic and he grew up to become the Jedi Knight, while his father disappeared searching for the mother who was captured by the Empire. The child who was captured was sent to Sith training at a very young age upon exhibiting force sensitivity.
My Sith Warrior was too young to remember what happened, and is loyal to the empire, but never exhibited the ruthless cut throat doctrine the Sith prize and survived on his strength in the force alone. He never really took to the teachings and thanks to the overseer accelerating his training and bringing him to the academy early, was never thoroughly brainwashed. Then during his time on Dromund Kaas and discovering the Light Sided Sith's teaching about the Light Side of the force, he has been studying the light side ever since. After witnessing the collateral damage of empire citizens due to Sith bickering and infighting, and the acknowledgment that the empire only survives thanks to the hard work and diligence of its military and NOT the power of the Sith, he is attempting to bring a new more lawful and compassionate Empire into existence.
My Jedi Knight is another story. While he doesn't remember his father, before leaving to search for his mother his dad did leave him a holocron detailing the crimes committed against them by the Sith. There resides a deep hatred and contempt for the empire that he hides well. So while generally compassionate and merciful, my Knight finds himself unable to show mercy to the empire and deals with them in a brutal and efficient unwavering manner.