Hi Mary! Welcome to the Disney Parks Moms Panel!
MagicBands have completely changed the landscape of Walt Disney World Resort vacations for the teenage set because no longer do you have to worry about them losing their room key or park ticket. Everything is all lumped together in one awesome piece of wearable technology.
Any and all
Disney Dining Plan entitlements belonging to persons in the same reservation are lumped together in one digital pot, if you will. This means that when everyone in your party goes out to dinner together, only one person's band at the table is needed to pay the tab/deduct the correct amount of dining credits for everyone. So yes, everyone on the same reservation is linked to each other.
You do have the options to allow or deny individual bands certain privileges like charging meal and snack credits, or allowing anything from food to haircuts to souvenirs to be charged back to the credit card on file. While everything at Disney changes all the time, the last time I asked you couldn't restrict dining plan entitlements to only a certain amount per day per individual band. However, you can set a monetary spending cap of credit card charging privileges per day so that they do have some way of getting water, lunch, or a Mickey shaped treat. This can be set up at your Resort Hotels front desk any time during your stay.
I hope this helped with your planning a bit, Mary, and we'll see you real soon!
~Kristen