BevS97 had some good ideas. I would make up your itinerary and send it out to everyone long before the trip. Tell everyone that you don't want to force anyone to follow your schedule but that if they'd like to join you for any part that they may do so. That way you can make sure you included all who want to be for PS reservations, etc. Plus you may want to schedule some time for your family away from everyone if you think you need it.
Definitely plan a couple of events that you all will attend together. You may want to call WDW because they have some specialists for large groups that could give you ideas. I would think a waterpark day would be fun where you could all plop your stuff down together for the day. Maybe meeting at SpectroMagic and sitting together would be a good idea as well.
Definitely use the radios to communicate throughout the parks. You will spend your whole day waiting for people otherwise. This way you can see if anyone is in your area of the park and you could meet up at a ride.
You will definitely want to make sure you try to schedule the most time with the Australian crew since it is a rarity to see them. Plus they must have spent a small fortune on airfare alone.
I'm always the "planner" but I also don't want to become the vacation nazi that everyone hates so I let everyone know up front that I want everyone to do what they want but offer my plans to them. I think everyone appreciates that. Good luck!