#in-universe I think her name is Arleen (as Joyce says)

[coraniaid]

The wiki claims that Buffy's "Aunt Arleen / Aunt Darlene" (spelling and pronunciation varies from episode to episode) is Joyce's sister, but is there actually any compelling in-universe reason to think that? Joyce herself never uses the word "sister" in either Choices or Pangs (in fact she's not even in Pangs): when she mentions her to Buffy she just calls her "your aunt", and that's also how Buffy refers to her in Pangs. Isn't it possible that Arleen is Hank's sister, not Joyce's?

True, Pangs tells us that Joyce is spending Thanksgiving with her, which implies they're at least moderately close. But Hank and Joyce's divorce doesn't seem to have so very acrimonious that she couldn't have remained on friendly terms with his other family members. And she'd have been somebody Joyce knew for almost twenty years. Maybe they started talking again, after not speaking so much for a couple of years after the divorce, when Joyce called her in Choices to talk about Buffy's Northwestern offer? Maybe that's why she got invited out to Illinois for Thanksgiving a few months later? (From Buffy's description of it in Pangs, it doesn't seem to have been a regular invitation.)

Obviously the writers don't care about this question at all -- they can't even keep Darlene's name constant, and she's only mentioned in two episodes! -- but I think maybe that would explain why we don't see Arlene at Joyce's funeral in Season 5? I mean you can argue that she was there but just in the background, but if your literal sister died (and you hadn't had some sort of bitter falling out) would you really leave all the funeral arrangements to her college-aged daughter and not even offer to help?

I am similarly convinced that Joyce's parents have to be dead before the show begins; the fact they're not at the funeral or seen in any background photographs or ever mentioned in passing seems too strange otherwise. (In Season 7's Get It Done Dawn does describe something as smelling unpleasantly like "Grandma's closet", but ... well, that could be Hank's mom too? And if not there's plenty of other stuff in Get It Done I'd be happy to ignore as canon anyway.)