When this woman is annoyed with her sister's partners, she asks Reddit:
My sister has apparently been in a polyamorous relationship with another couple for several years and only recently disclosed the nature of their relationship. When I thought they were just friends I hung out with them twice and both times I didn't really like them.
My sister kept trying to invite them to small family-only events, which annoyed me and my family but no one wanted to say anything to her. She finally claimed to be in a relationship with these people when she tried to invite them to my parent's camp in summer 2020.
The camp is very small with close sleeping quarters and not enough room for everyone, so I told her I didn't want them coming. Covid was also a big issue. Also they came the previous summer and it was horrible.