Here's the background: my family is spread all over the world and a lot of them have children. I know from experience that it's pretty rare for any of the families being invited to travel together. So for example, one spouse and one child of a five person family may go one one trip while another spouse with the other two kids may take a trip somewhere else on another date. I want to include something on the RSVP cards that tells me how many individuals from the family unit being invited are coming (and, if possible, which ones). Is there a way to do this?