Great advance planning, friends certainly come in handy at these times, lol!
I would plan ahead for autographs (if they are getting them) and invest in a nice book where you could also place a pic of your DDs on the opposite page of the character for a memento to cherish.
The night before I would have something waiting for them in your room-like their tiaras (if they don't know about them already) with an elegant invitation to dine at CRT the following morning. Or (I did this for a friend's daughter) purchase a charm with the carriage/castle and add it to/start a charm bracelet. By the end of the trip she had a number of small silver charms and a neat souvenier for years to come. Since you were also talking about
Disney cruise next year (on your other thread) they could add more charms later. I bought the charms off eBay.
You could get them a miniature Cinderella (or their fave princess doll), just search eBay for Disney miniature (and the princess name), I've gotten them as inexpensively as .99 + shipping.
Another item I saw when searching eBay was a cute Cinderella purse:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=44034&item=5979187537&rd=1&tc=photo
That would be cute, not sure if your girls are into that though.
I've heard it is best to bring a change of clothes for afterwards, not sure what your touring plans are.
GL making your PS-hope you get thru!