Hi Angie! I can appreciate your desire for your daughters to understand some of the Disney characters before your upcoming vacation. Many parents don't want their children to be afraid of these bigger then life mostly silent characters greeting their little ones for the first time. They want the experience to be magical!
Disney movies are generally quite long and your daughters would most likely would lose interest quickly. I suggest you introduce the main characters such as Mickey, Minnie, Donald, Goofy, Pluto, and princesses through story books or perhaps the Disney channel. Mickey Mouse clubhouse is a great beginning intro into the world of Disney for toddlers and there is a wonderful Mickey Mouse Clubhouse attraction in Hollywood Studios where they are encouraged to dance and jump around.
There are also some opportunities to the characters via the Disney website,
www.disney.com or clicking
Here to reach the character page. Introduce them through pictures and if you can add singing some of the wonderful Disney music to your days this will really get them excited when they reach the parks and hear the same songs.