Hiya Chris - welcome back to planDisney!
I have some great news for you about
Advance Dining Reservations! If you're staying at a
Disney Resort Hotel, you'll be able to start making reservations 60 days in advance! At that time, you'll be able to make reservations for your entire length of stay, up to 10 days.
The really good news is that other than allowing you to book for your entire length of stay, there isn't any other link between your Resort reservation and dining reservations. So, that means that one person can make the reservations for a party of six without the need to coordinate. If one of your two families is checking in to their Resort one or more days earlier, this is the person who should make the dining reservations, as they will be able to access reservations sooner.
Chris, while most restaurants can easily accommodate parties of six or more, you may still run into some limited availability, especially for more popular options. Sometimes, you won't be able to find an available reservation for six but can find one reservation for four and another reservation for two at about the same time. I know that's not ideal, but that can be a good way to still experience a popular dining location!
Just remember that the system doesn't allow one Guest to hold overlapping dining reservations. You'll just need to have someone else in your party book the second reservation, and be sure not to link the original reservation to the My Disney Experience account of the person making the second reservation (i.e., leave it as "Guest 2"). If you end up going this route you can always stop by the restaurant in advance, let them know about your two reservations, and request that you be seated at the same table or nearby tables. Cast Members will do their best to accommodate you!
I'm sure you've already done your research, but there is one option that I definitely recommend, and that's
Topolino's Terrace - Flavors of the Riviera. Whether it's an elegant dinner or the magical Breakfast à la Art with Mickey & Friends Character Dining, this new signature restaurant perched atop
Disney's Riviera Resort never disappoints!
Ryan J.