Can you imagine their social medias if they add all their siblings, nieces and nephews, cousins etc. I have over 300 friends just from having a normal amount of cousins who're old enough for it (1 sibling whose childless, 10 cousins from both sides of my families and thats only because 1 of my uncles has 5 children, the rest have between 1 and 3) plus school friends, university friends and some work connections (although I tend to remove people after I no longer work somewhere). They'd have over 100 connections before you've even added any of the others! Wow!This happened a few generations back in my family (huge family because of no contraception and an abusive husband). Several first/second cousin marriages were narrowly avoided because there were so many people and such loose connections between the oldest and youngest that nobody knew they shared one common grandmother/great grandmother.
Of course, now you have the internet I suppose its easier to trace family......but still......