The larger the party gets, the tougher the FastPass availability is for many rides. No worries though, we have successful reports of up to 19 people at Christmas using the Line Hacks System.
This all depends on the ride and the difficulty levels. If it’s an easier ride, groups under 6 people should get good results. If it’s a tougher ride, you should consider breaking into groups of 3-4 max and then hacking for overlapping times. This goes for Day of Drops as well.
If you have a larger party, I recommend having more than one person hack at a time! Check the next FAQ for more details.