I'd have been really annoyed if I'd gone to the trouble of checking in online so I got a decent seat and then finding out that I'd been bumped because of a family who couldn't be bothered to check in online. You know they do online check-in so why did you expect all the other passengers to move for you? You could have thought "we want seats together so lets check in early online".
Personally I'd have been miffed if I'd had to move because of someone else being lazy and expecting me to move.