LogFAQs > #970926743

So I'm going to try and make this as short as possible, since I want an outsider's perspective on a huge meltdown between my friends/family.

A friend of mine (and her boyfriend) were renting my parents' basement for about a decade, and as a result became incredibly close with me/my wife, my parents, and my sister & bro-in-law. They effectively became part of the family.
Full disclosure here, my sister and her husband are anti-vaxxers and have a lot of bad medical opinions. The family-friend disapproved of that for years, but looked past it and tolerated it because they were still good friends.

Fast-forward to the post-pandemic era... In 2020, when everyone was working from home, these friends were working from home at my parents house. At the same time, my sister would bring her kids over a few times a week to use my parents' pool and to play with friends there. One seems to be a little behind, in social development, and the friends (one is a licensed psychologist, seemed to believe this as well) and as a result, the kids together are very loud and rowdy. The friend frequently complained to me about how loud the kids are, and was shocked at how my sister would bring them over severalt times a week like clockwork, during the summer, saying that it was distracting while she worked at home. But she never confronted my sister or said anything to her about it.
By the end of that Summer, this friend and her boyfriend bought a house and moved out. Sadly, in that same time period, her mother passed away from COVID. Similarly to the kids thing, she complained to me about my sister being anti-vaxx and how that's insensitive especially in a pandemic, but once again never confronted my sister/brother in law.

So NOW, finally present day, in the last 2 years, the friend 100% completely ghosted my sister/bro-in-law, even though they were some of each other's closest friends, but continued to be friendly towards me and my mother (whom she cites as a second mother to her, after her own passed away). When we asked why, she says it's because they're bad people, and that they abuse my mother by using the pool all the time and having my mother babysit the kids all the time. She doesn't cite the anti-vaxx opinion. And furthermore, again, they never had an argument or a confrontation over any of this. Just at some point in 2021, they decided to ghost.

But the ghosting has gotten progressively worse, to the point this friend and her boyfriend won't show up to anything that they're aware my sister will be present at. She won't even humor it to see everyone else. And now this makes it incredibly awkward for me and my mother, because we'll invite her to parties, and she'll initially say yes, but then days out if she finds out my sister attends, she'll change her mind. She talks shit about my sister and brother in law to both me and my mother, in spite of the fact it's her daughter lol.
And worst of all, IMO is we very very recently discovered that for all our other friends, this drama-friend never told any of them that she ghosted my brother in law/sister. Rather, she started telling people things like "I think they've gotten very inwardly selfish over the past few years... They don't like to show up to anything anymore... They don't reach out to anymore... It's so weird." So as a result, the rest of my friends kind of bought into that narrative, and don't really invite my sister and her husband to anything anymore, and as a result, they feel like every one of our friend group hates them, when really it's just the one.

BASICALLY, this is a long-winded way of me asking, where do you think I should go from here? I never had any issue with this friend, and she & her boyfriend still talk to me buddy-buddy like there's no drama going on. But it's super awkward! And after finding out she effectively poisoned our other friends against my sister, it was a huge turn-off. Should I still stay out of it and keep associating with this person? Or should I ghost her back?

tl;dr version in Post #2