They only see each other about once or twice a year , so it's a pretty good bet they'll be friendly and polite. They're all so different that I'm sure they would never pick each other as friends if it weren't DH & I being married.
There was one "rough spot" between my DMand my DFIL. It happened at our wedding reception in 1990. DFIL made a pass at DM. He had one drink too many, she was offended, but handled it well without making a sceen (during or after). It never came up again, never happened again, and everyone (who knows about it - DMIL doesn't) acts like it never happened.
It's pretty easy to keep things peaceful when 2 are in NJ, 2 are in FL, and 1 is in NC.