When I was making all of the arrangements for our grand gathering last year, my family was so surprised when I would get on the phone at 6:58am my time to get our Priority Seatings. However, while we were on the trip they were so thankful to have a nice place to sit and eat a good meal during that hectic Thanksgiving week. We didn't tour the parks together most days, but it was nice to be able to get together mid day or in the evening to swap stories and relax a bit. Plus, I can not stand to eat counter meals constantly. I have a more restricted diet a sit down restaurant gives me more choices. During our first 2 trips I found that if I didn't plan the meals, we wound up eating at the food court at our Value Resort. And that gets old fast (unless you count breakfast! Yum.)
You may be able to get something last minute as I'm sure they hold some openings for last minute availability, albeit nothing for 10 people. Hey, you can always just plan to get together at a counter service spot during an off hour and eat together. Takes a bit longer, but at least you're together. Have a great time!