I feel for you - and anyone with older relatives who are appearing so blasé about it all. I think until
they feel the anxiety and reality of it all, theres' no amount of nagging in the world that will persuade them to stay put. However, you could always make them feel guilty by saying that they are putting the family at risk, or plain old "If you insist on going out, I have to keep my distance". Obviously its hard for them, and also us, but you need to keep yourself strong for the rest of your family, and if you are stressing about what is essentially someone having a strop because "No bloody government is going to tell
me if I can go out or not" then you need to have that conversation with them