It's....It's a different character? People can have more than one relative.
Her uncle works in the fishery and her aunt works on the docks, from what I can tell.
No they're the same character, the uncle now aunt lived alone before Furuka crashed there. The author retconned the character into being a woman.
Citation? I'm not saying you're wrong or lying, but there's nothing in the manga that indicates that. The uncle can live alone while also having a sister who lives elsewhere on the island. They have different jobs and different appearances, and we've never seen the aunt at home with Furuka.
I just don't know where it's coming from. Have the early chapters actually been changed in the tankoubon? Did the author say something about it somewhere? Or are people just making assumptions because the aunt started showing up in the last few chapters, and the uncle hasn't been seen since the early ones?