My ILs and my parents "know" each other by sight - but even when they lived in the same town, they moved in different social, business, and church circles. So they are more acquaintances who happen to have grandchildren in common than anything else. I don't think that they have socialized since we moved out of that town and no longer have "open house" drop ins. My parents now live an hour or so away and go back to that town only for specialist medical treatment (larger town with more specialists practicing).
I have been out to Ambrosia Hino's IL's (FIL & SMIL) for Thanksgiving twice and out to dinner with the family two or three times. I was by myself with a house for sale in the area the first time and doulaing for the new grandbaby in 2010. I've also been with them when they met with CrazyMIL in the past, but she's been dropped from the social circle since the bat poo hit the fan....... I did see FIL & WonderfulSIL's step sister (hard to figure out too many letters in a row) the last time I was there - but his SMIL and step brother were in class or at home (respectively), so I didn't see them.
I'd say I still see more of them than my parents and ILs see of each other.
My father's parents and my mother's parents didn't socialize much - but they did send each other home canned jellies & such - depending on who had the space for a garden & time to can at the time. Looking back - that seems to be the way MOST families I knew had their grandparents interact - at a remove and through the grandkids, if at all.
Now - Dad's family tree has about six surnames that keep repeating, generation after generation - back to the late 1780s (Mom was showing me the geneology this weekend) - but that is probably due to the family being in a particular region back when travel was a lot harder. But Grandpa and Grandma both had names that had been on the family tree several times.
Dad's mother's family reunion has cousins on his father's side of the family who show up because they are cousins, too - just not descended from the person that the family tree is supposed to date from (came over on a boat to Ellis Island in the 1880s) - the guy on the boat was a cousin to their ancestor, though, who came over on a different boat.
I mentioned about six names that keep cropping up through the family tree, right? Those are two of the three surnames that show up most often. That side of the family was all into farming in a small area in Texas and they still interact at the various family reunions a lot!