AIBU in thinking this is a little strange...parents of adult children befriending their children's friends, to the point that they end up catching up with and doing activities with their adult children's friends without said child.
I know no-one 'owns' anyone and people can be friends with whoever they want, but I've never come across this before. Where say grandparents end up taking over their grown children's friendships and end up hanging out with a bunch of people 30 or 40 years younger than them.