You're allowed to block 20% more than you guarantee and the guarantee is generally based on the number of guests you have. I believe it's 25 nights for less than 40 guests, 50 nights for 41-75 and 75 nights for 76+ guests.
I think they are flexible and will work with you, so if you have concerns you should bring it up to your consultant.
Keep in mind this also includes your own room. To meet a 25 night guarantee you would just need 4 families to be staying at Disney for a week. So really, if you stay at Disney for a week it would only be three more families.