It is one person per card with Amex platinum. So unless the kids and wife each have their own card they will have to pay the 29 guest fee to get in the sky club. They could all go to the centurion club for free with the card. The accounts don’t have to be different but each person does need a card. I think you can have three additional cardholders for about 200 so it is not a bad deal to add card holders