Each room key can access all the credits for the room at anytime. As far as park ticket media, you can add whatever type you like (except APs) to the room key as well. You can even buy them from an authorized seller, like maple leaf or undercover tourist and have them on your room key. SImply present your park ticket and the room key at the concierge desk in the lobby and they can transfer the ticket for you.
If there are any children under the age of three, they won't get a room key and you won't have to pay for tickets or the dining plan for them. But if you order them food, you'll have to pay out of pocket for that.