Can I put birthdays for two different people on a card in Contacts?

I have some cards in Contacts which relate to two people - in a few cases, four people. Is there any way of putting birthday entries in for all of them which will come up in iCalendar, short of giving each of them a separate card in Contacts? That seems a bit over the top for my God-daughter, for example. She's four. Her little brother is only 2!

Just put a recurring date in Calendar. No need for Contacts.

A perfect solution. Many thanks