Hi Thomas
A September family vacation to Walt Disney World Resort sounds awesome. I remember a few years ago, when my family, my sisters family and our parents, spent a few days together. We had such a great time.
I love the
Disney Dining Plans. It means no worries for the rest of my vacation; problem free, Hakuna Matata. The entitlements are linked to your Resort hotel account and easily accessible with your
MagicBand. To answer your question, basically yes, but I'd like to add a few points.
If you are dining at a Quick-Service location, you can simply make separate orders. For a Table-Service location, simply inform your server that you wish to charge the meals to separate accounts, and also indicate that you'll be using a dining plan entitlement. They will take care of the rest, and split the bill accordingly. Now, if your grandson is a minor and nobody else from his reservation will be dining with you, make sure that he has charging privileges. Simply stop by the concierge desk at the Resort hotel ahead of time, so you won't have any issues.
Hope you have a magical time and I'm sure you'll make lasting memories.
Ricardo.