How exciting!!
Set expectations early on as to exactly what you will cover. Figure out your line item estimates on your own for somewhat fixed price items like tickets and transportation. That leaves you with rooms and meals. You will know what you have left in your budget after the above items. Personally, I would plan on QS and do one or two special ADR's. Don't forget snacks.
If you have multiple rooms you will have more choices with dining or ticket options.
All guests in a room must all be on the same dining plan. I think planning for fall may give you more choices. Free dining would be a huge benefit to you if you can secure it as even QS will be 1K a day,
conservatively for nine.
Location is key. What you are willing to spend on accommodations will make or break your trip (from 52 years experience). Being on the monorail will give your family many options and more importantly time...more time to hang out at the pool, nap and be on vacation!
Mydisneyexperience is where you plan who will be with you (they can be in different rooms) and your plans will show on your itinerary. You can share with all your family members so they can see it too. There is even a place for you to make notes for each day (meet for fireworks tonight, pool break today, etc)
Plan loose itineraries. Don't expect everyone to be together 24/7. A night out for the young couples might be a nice gift. Take your time and let the kiddos explore. Unplanned surprises are often the highlights of trips.
This is not comprehensive, but hopefully it is a start for you! Enjoy!