Well my sister is a bit annoying (all little sisters are), but no, I can stand her. Her MIL is, how do I say it, vile. When my sister was dating her husband he invited her and my nieces (with him and his daughters) to go to Florida for a vacation. His parents were there and they paid for a big family dinner out, except they wouldn't allow my sis and nieces to eat with the "family" and they had to stay in the hotel while everyone else had dinner together (and BIL left her there). She did break up with him for a year or so after that, but whatever they got back together and got married. This is just one incident among many. They viewed their son's second marriage as living in sin as he had a Catholic wedding the first go round and they didn't recognize the divorce.
As far as said BIL's mother, she's gone downhill again and is on the max oxygen they will give her before a ventilator. Next time I talk to my sister I'm going to ask her if she's changed her own personal stance on getting vaccinated.