Through the first 8 Star Wars episodes, we only see two sets of scenes with Uncle Owen and Aunt Beru.
In A New Hope, Owen tries to dissuade Luke from consorting with Old Ben. We get a sense that he at least knows Ben's true nature. No other reference to Luke's relationship to Anakin is explicitly referenced in this film.
In Revenge of the Sith, we see baby Luke get adopted by Owen and Beru. But it is unclear how much they are told.
My question is, did Owen and Beru know that Luke was the progeny of Anakin?
As pointed out, these very well could be relatives of Anakin (although I wonder if Aunt and Uncle are token titles)
I am really wondering whether they know Luke is Vader's son.