I have put together 2 large party vacations for us; one was a group of 11 and one was a group of 17. WDW tries very hard to accommodate large groups. We have sat together at most places and the few that couldn't, did seat us at adjoining tables.
At Via Napoli, there is the communal dining table that is long and seats a ton of people. I would imagine that is where they would seat you.
I agree with PP, at LTT, you will more than likely be seated at 2 round tables for 6 that are next to one another.
You can make your reservations online for groups up to 14. No need to call the special dining line.