Or you avoid the topic, keep your fingers crossed that they won't get sick, and can at least have a normal conversation about the weather without hating each other.
That does not help your relationship, because interpersonal relationships where you can't express your honest feelings and ideas are hollow, fake – worse than useless.
That doesn't help anything about COVID, because they're still acting recklessly based on their delusions.
And that doesn't help their deteriorating mental ability as they succumb to propaganda, because their idiocy is left uncontested, only reinforced by their self-selecting ingroup.
At some point you gotta choose what you actually love about such people – their meat and bones, your nominal connection to them (e.g. blood relation), your past shared experience, their personality and ideas, or something else? Because some of those are unaffected by their progressing stupidity and selfishness, but others are poisoned more and more as time goes on and they sink deeper.
I don't have a solution. I just wish people would stop pretending that this brainwashing can be solved by talking, understanding, or simply by ignoring its existence. Often it can't. As a society we're in deep shit, and it has little to do with COVID. It will stay with us well after the pandemic too.