If two people walk towards a single person, coming from the opposite direction, on a narrow side walk -- who should give way ?

Most normal people yield space if they are not in "their" space. But that definition is changing with diversity & mannerly rules related to left and right. That complicates it some. Not unlike the recent media reports about the American diplomat in England driving on the wrong side of the street.

But "manners" themselves are taking hits in many places around the world. Especially, it seems, in the U.S. people accustomed to having the right of way in all things are feeling challenged by things like the pandemic, economics, etc. and that can be a distraction that can result in some walking down the middle of the sidewalk without thinking about manners to aggressively trying to claim the "rights" they feel they are losing in symbolic ways by asserting their will on others.

each person should move to their right....the couple goes single file

the younger and healthier ones

Someone not looking for a potential fight. And dont view that as a good thing. Its better to just avoid. It doesnt make you weak or anything. Its a good thing to not be violent and wind up in jail potentionally and a threat to the public.

In light of the pandemic and social distancing, I would go around them.  In my area, most people walk on the street.

try googling ‘sidewalk etiquette’