I don't know better, but I believe that perhaps people could even agree to leave one by one. As in "I'm leaving now and taking the initial heat. You stay there until the time is right. Now you get out, too, and make sure we bring so and so...".
Twitch, I was just thinking about families where everyone is a witness (worldly relatives having been forgotten one or two generations ago). Someone has to get the snowball rolling...
Little Witch, I understand what you're telling YKnot. But maybe everyone needs to do things their own way, as their own particular circumstances demand. Me, I will be very, very happy the day I will finally hear from YKnot saying ALL THE YKNOTTIES are out!