Hi there Sue,
Let me start by saying that Christmas is one of my favorite times to visit Walt Disney World. The parks are decked out in their Holiday finest with twinkling lights and sparkly decorations and familiar jingles fill the air. Several special Holiday events take place around the resort, and the December temperatures are cool and comfortable!
As far as tickets are concerned, I highly recommend visiting the official
Disney World Ticketing site to purchase your park tickets. Here, you will be able to browse available options to decide which ticket will best suit your party's needs! SInce you are going to be in the area for a week, I suggest considering at least a 6-day Park Hopper ticket for each member of your group. The Park Hopper can be added to give you the flexibility to visit multiple parks in the same day!
At Disney, the more you play, the less you pay, so I think you'll be surprised to see that you can add additional days at a very minimal cost!
Best Wishes,
Amanda F.