Maybe you should let go of the feeling that you are responsible for what these other people believe or chose to do. If you don't want to go to Thanksgiving with 20 people, simply don't go.
If my mother is no longer competent to reason on her own, it is my responsibility as the eldest male in the family to take responsibility. Is it not? This is the job of the middle-age: the turnover point where the children begin to take care of their parents (instead of parents taking care of children). As the elderly lose their mental capacity, it falls upon the shoulders of my generation to take care of them.
> If my mother is no longer competent to reason on her own, it is my responsibility as the eldest male in the family to take responsibility. Is it not?
Believing this particular set of lies is not, however, a reliable market for mental competence. You yourself note how widespread these ideas are among your family, most of whom are presumptively mentally competent adults.
Any chain of reasoning that leads to a conclusion like "half of the country is mentally incompetent" should be suspect.
In a way, this whole situation is where a whole suite of ideas like postmodernism, epistemological/cultural/moral relativism etc., come home to roost. After all, these are just alternative facts, and what we hear from so-called experts is just, like, their opinion, man.
What I'm saying is: my mother's wellbeing will soon be my direct responsibility.
Obviously I'd rather have my mom take care of herself... Less work for me. But her ability to handle money has appreciably degenerated, and now this COVID thing is proving to me that she is unable to fully analyze the news on her own.