Keep in mind that for first timers, Disney can be amazingly overwhelming. Ask them to make a list of what they want to do and they don't even know where to start. It becomes much easier to say "oh, you make all the plans, you know what you are doing - we will just tag along." And this can work fine if your friends have the same taste as you, the same budget and work at the same pace - and can be difficult if they want thrill rides and your favorite thing is Small World, you want to stay at the Grand Floridian and they are fine off site at the cheapest place they can find, and you want to be at the parks at opening and they are "vacation! we aren't moving before 10am" people.
So start by defining what type of people everyone is in terms of budget, pace and taste.
It might be easier to give them limited choices. "We will be in Epcot this night for dinner, which one of these restaurants would you like to go to?" Or general choices "would you rather spend a day riding thrill rides at MGM, or would you rather spend a day over in the MK doing tamer stuff?" "Would you rather spend an afternoon at the waterpark, or would you rather redo your favorite rides?" "Do you want to do Pleasure Island or Cirque du Soliel or would you like to turn in early?" "Do you want to watch parades, or would you rather see the attractions?"
Also, try to "orient" them over the first couple of days, and then encourage splitting up. Play tourguide on days one an two, by day three they will be familiar with how Fastpass works, how the themeparks are laid out, how to read a map. Or at least, revisit plans as a group a few times during the trip.
So start by defining what type of people everyone is in terms of budget, pace and taste.
It might be easier to give them limited choices. "We will be in Epcot this night for dinner, which one of these restaurants would you like to go to?" Or general choices "would you rather spend a day riding thrill rides at MGM, or would you rather spend a day over in the MK doing tamer stuff?" "Would you rather spend an afternoon at the waterpark, or would you rather redo your favorite rides?" "Do you want to do Pleasure Island or Cirque du Soliel or would you like to turn in early?" "Do you want to watch parades, or would you rather see the attractions?"
Also, try to "orient" them over the first couple of days, and then encourage splitting up. Play tourguide on days one an two, by day three they will be familiar with how Fastpass works, how the themeparks are laid out, how to read a map. Or at least, revisit plans as a group a few times during the trip.
We are planning the first ever family vacation with my side of the family. We will have a total of 8 adults and 5 children (ages 2-10). My family have been 3 times, my sis and her family have never been, my bro and his family - once and my parents haven't been since we were children (I think that was 1978) 
. We are all staying at the WL but in separate rooms and not requesting ajoining rooms. Probably won't even request rooms in the same area - just luck of the draw - wherever they put us. We've also had many discussions on how we don't have to be around each other 24/7. If one family wants to go to the waterpark and another doesn't - fine - won't hurt anyone's feelings. Hope that will be as easy as it sounds! 
Any suggestions?
But it was not what I had planned and I did not have the close togetherness with my own little family that I am used to. They also slowed us down. My family probably would have seen @ 50% more if we had been by ourselves. I had to make my peace with this early on in the trip, or it would have been a disaster.
