Currently, each KTTW card will contain ALL the credits for the entire reservation. For instance, 5 people X 4 nights = 20 credits. So Mom's card will show 20 TS, 20 CS. 20 snacks. Same for dad and each of kids. When a credit is used it is deducted from all cards even though only one card is presented. There is no need for everyone to eat together. If you all eat together, you need only to present one card.
There are many rumors flying on the boards as to how WDW is going to change the plan to eliminate cheating. The most likely thing is that they might separate kid credits and adult credits. However, at this moment a credit is a credit--no separation in the computer of kid vs. adult.
You can eat together, you can eat separately--it doesn't matter. The teens can go to McDonald's one night and you can go to a signature restaurant.