Yes. In the film "A New Hope," Luke and Obi-Wan learned that stormtroopers slaughtered Jawas that sold Luke's uncle R2-D2 and C-3PO. Realizing that the stormtroopers would have learned whom the droids were sold to, he rushed back to his uncle's homestead only to find it was scorched and saw the skeletons of his aunt and uncle
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Luke Skywalker was actually born on Polis Massa as his mother and Obi Wan were fleeing the Empire. After Luke's mother died in Childbirth, Obi Wan split the twins, Luke and Leia, to insure their survival. Luke was sent to Anakin's step-brother on Tatooine and Leia was taken to Bail Organa on Alderaan. That is where they grew up until they joined in the Rebellion against the empire.
Obi Wan Kenobi brings Luke to Owen Lars and Beru Lars on Tatooine, who agree to adopt him. They are his step-uncle and step-aunt as Owen's father had married Anakin's mother, making Owen and Anakin step-brothers.
He left Tatooine because when stormtroopers burned down his home and murdered his family, there was nothing left for him and no reason to stay
His uncle is Owen Lars and his aunt is Beru Lars (nee Whitesun)
No. Luke never turned to the dark side. Only his father did. Of course, that's only true if you completely ignore the extended universe comics and novels that not only feature Luke turning to the dark side once a resurrected Palpatine appears, but had him breaking free and becoming a full Jedi master by way of the experience.