S.B.
Disney has 4 theme parks: Magic Kingdom, EPCOT, Hollywood Studios, Animal Kingdom. At Disney, you can buy Park Hopper tickets to visit more than one park a day. Each park offers something special for the holidays so you might want to research what you want to see most. All of the theme parks (inc Universal Parks) are crowded during the holidays, but it is really a unique experience. I would spend 2 days at Disney, unless someone has their heart set on seeing the Harry Potter exhibit at Universal. The parks are crowded, but the only park that usually shuts down is the Magic Kingdom on Christmas day because many families want to take their kids on Christmas morning. Have a wonderful trip!