Address book, different contacts with same name

[newtoiphonesdk]

My wife and I both have iPhones and we sync the contacts from Address Book. We each have our own group, so that our contacts aren't too large. The problem is with our parents. We each would like our parents to simply show Dad and Mom. For example, my group has Dad Mom and Morris and Sheila (her parents). Her's has Dad Mom and David and Carol (My parents). The problem is that though we created these as different contact cards, it tries to combine the Dad and Mom contacts every time we sync again. Anyone have suggestions for how we could fix this?