Hi Julie,
Walt Disney World's Vacation Packages are based upon rates for a family of four. For information on these, check this webpage:
2013 Magic Your Way Packages. You will be able to choose packages that provide Room & Park Tickets only, or Room, Park Tickets & Disney Dining.
For your family, I would recommend that you purchase 2 packages, allowing one of the children to be part of the package with the grandparents. That will place you in two rooms and allow you to have all of the privileges of the Magic Your Way Package for everyone. If you decide to stay in one of the Disney Vacation Club Resort Villas, there are options available that would sleep up to 12 people per villa.
In addition, if any special deals are offered (though if they plan to have special deals during your travel time, they have not been announced yet), you will find those on this webpage:
Walt Disney World Special Offers.
If you have purchased a package and a Special Offer is announced at a later date, the deal will be applied to your package. Make sure you contact Disney Reservations to make sure this adjustment is made to your package rate.
I also recommend that you look into the Disney Dining Plan. Our family enjoys the savings it provides because we love to dine at the spectacular restaurants and enjoy several Character Dining Experiences. You may make your Advanced Dining Reservations up to 180 days ahead of your visit, and I recommend you do so to make sure you get the reservations you want.
I hope this helps you get started in your planning. Once you have looked at all of your options, we are happy to assist you if you have more questions. We wish you a magical vacation!