How Luke has an aunt and uncle if Anakin was an only child?
They aren't related to him by blood, but yeah, their dad bought Anakin's mum as a slave but then married her.
After the events of Revenge of the Sith, I suppose the only option for Luke was to leave him with them, being the closest thing he had to family available at that point, and Obi Wan knew they were good people I guess? Padme/Anakin must have mentioned them to him at some point. Not in the movies, behind the scenes. Where all the characters go and party when we're not looking.
Owen is indeed Anakins step brother but even if he wasnt Amidala has a sister.
Kefka's coming, look intimidating!
Have a nice day!!