I am thankful that I don't have any of my close relatives in the same camp as your sister, but I know my husband's cousin and his family are like this. They're also anti-vax'ers so we've already gently let his mother know we are not inviting unvaccinated guests to the annual Christmas party.
We've been polite to them at past parties, but now that their political choices might put our young niece at risk (she's too young to be vaccinated), we're drawing a line. Maybe we should've drawn the line earlier? Thanks for the thought-provoking essay, John. I'll see you in Hell as I'm also in the same boat.