Q: Birthday Calendar and Contacts

I have a family of 2 parents and 2 children which I would like to add to my Birthday Calendar through my Contacts.  I have entered one of the parent's date in the birthday field but is there a way to add the 2nd parent and the children to the same contact card along with their birthdays.  I don't need a card for each of them; only one card for the entire family.  Do I add an additional birthday or a date in the "other' field? I also need to customize the name to know who's date is who's.

In the end I would like 4 individual birthdays associated with one contact card and to then have those birthdays appear in my calendar.  Is this possible? I have Contacts 9.0 and Calendar 8.0.