This is another one of those many things to which I’ve never given a moment’s thought.
Luke lived with his aunt & uncle, they had a moisture farm, he wanted to move out, they have a few lines, they were killed early in the film.
It took me longer just now to peck out that sentence than I’ve spent in the past 40 years wondering about their backstory or familial connections. To me, this is just more of the damage Lucas inflicted on the franchise when he decided to shrink the universe.