Oh, gosh, that sounds awful. And I'm sorry for what your family is going through.
I would neither smack them down nor say something like "I can't deal with this" (which would invite speculation and maybe gossip that you are falling apart). I'd just interrupt fairly early and say something like, "You know, I just really am tired of talking about this. I'm sure you understand. But it's so nice to hear from you -- let's talk about something else. Are people in your area wearing masks and social distancing/How is your dog/daughter/garden doing/can you believe what Outrageous Public Figure said yesterday/etc.?"
In other words, just politely ask for their help/understanding and change the subject. I'm sure you'll know what topic they will be unable to resist.