Here are some things to consider:
* I love the Unofficial Guide-- it is a great tool to obtain a depth of knowledge about the parks/rides/restaurants/ etc. I find it is especially useful to research the rides...make sure they are appropriate (we will never go on the Stitch one!), find out if there are height restrictions, etc. This will help everyone decide on their "must do" list for each park.
* consider the Bibbidy Bobbidy Boutique if your girls would love a princess makeover...from a glitter make up and hairdo to costumes. You can also get a glitter do at the Barbershop in Magic Kingdom.
* If they have their own princess costumes, pack'em up and wear them to the park -- or character meals, which are also a lot of fun to dress up for! Bring a change of clothes just in case.
* There are also fun things like tattoos, hair wraps, etc.
* don't foget to schedule time for swimming, shopping and shopping.
* if your girls are collectors, pressed pennies, autographs and pins are a lot of fun to collect throughout the trip (and trade pins w/CMs as well). Collecting autographs can take up a lot of time,so character meals are great for that. You can also collect autographs on pillowcases, bucket hats, etc for a unique souvenir.
* Disney has a ton of fun,silly hats everywhere and it could be fun to take pics of your girls trying on princess hats/gear whenever you can -- I have a great photo montage from our last trip of my kids in about 30 different hats! You can also do a pic of the kids in hats from each country in world showcase!
Happy planning!