You can have the credits places on whichever card (s) you want when you check in. For instance, you can specify whether you want the meal credits to be accessible from the kids cards, one adult, all the adults, or whatever. The only kicker is that all the credits can be used from whichever cards you choose. For instance, you cannot place only your teen's credits on his card.
If you are in more than one room, you can split the credits for each room--for instance grandma and grandpa on one, mom, dad, kids on another. In that case if you all eat together you will need to present 2 cards--one for each of the rooms. Alternatively, you can use all the credits on one card, but that might result in having no credits left on that room/card before you run out of vacation.