You do know that Christmas will be really really crowded - parks at capacity - right? And that it will be a lot more expensive for your accomodations?
What is your budget? How many days?
You'd need three rooms at a resort, unless you'd manage to snag a DVC Grand Villa (not likely for Christmas this year), or stay in a large suite (lotsa money).
The Christmas thing makes a big difference, because at Christmas time the parks often close due to capacity. If you are staying on site, Disney will guarentee you admittance somewhere (not always the park you want to be at, but somewhere). Offsite will mean you need to do even better time management, but you can probably find an house or condo more reasonably priced for your party size.