Hi Corrina, thank you for your note, and for joining our forum. Sorry for the delay in responding-- the holiday rush kept us very busy!
These are all great castles. The best bet for lighting all three would be our Pico LEDs, which are small enough to fit into a 1x1 LEGO brick or under a plate, which means you can put them pretty much anywhere. We sell a Pico LED Starter Kit which includes a power supply, adapter boards, cables, and 8 warm white Pico LEDs-- this would be more than enough to light either Belle's or Cinderella's castle, and you could order additional 10-packs of Pico LEDs and adapters when you're ready to expand (one battery pack will power 100 or more lights).
For both of these castles, there are lots of colored transparent elements that would look great with little Pico LEDs underneath. Again, you could probably do both castles with one Pico LED Starter Kit.
For the Disney Castle, that one has so many special parts and details that we're working on a specific kit for it. There's another topic in the forum dedicated to that.
I hope this information is helpful-- please let us know if you have any additional questions. Thank you!