Those are notable issues (though if you take Barks as canon Duckburg is intentionally in Calisota - basically Northern California but fictionalized; and it could make sense to try to 'localize that' for an audience elsewhere; especially when they're just "comics" - Don Rosa's detailed Life and Times would likely garner more respect) - but also note that if you step outside the Barks canon the stories get varied and wild, and are inconsistent amongst themselves. It's one of the surprising things about Don Rosa's work - not that he wrote it but that he COULD write it; Barks was internally consistent without apparently trying.
Lots of these things are caused by the Disney "rules" at the time - no human characters for example (everyone "human" is technically a dog), and there may have been additional rules about "real places" - though enough adventures involved GOING to real cities and locations.
Depending on which story you started with I could easily see the misunderstanding - the "three nephews" refer to Donald as "Uncle Donald" and to Daisy as "Aunt Daisy" at times - but if Donald and Daisy aren't married the way to make that work is to make them cousins. And then you get a second story to translate where it's clear they're dating, and you are now kind of stuck.