I was planning for a group of 9 and a lot of the restaurants at Springs have a limit on how many you can book online using Open Table. 8 for Jaleo and Raglan, 6 for Wine Bar George. On the WDW site there is often difficulty making reservations for a party of more than 6. For a party of 18 you will either have to make some phone calls, or have multiple people book multiple tables at similar times and hope they can merge you or seat you near each other.