you will pay full price for the daughters, unless they are under 3 yrs. of age.
There have been numerous threads on this (and similar issues) and the answer has always been that people were charged full price for everyone in the party...including when a child actually had a feeding tube (could not take anything by mouth) and also for adults that have had the weight reduction surgeries where they can only eat tiny amounts of food (like 4 oz total per meal) Even with doctor's letters they all still got charged full amount.
Part of the justification is that at least a portion of the cost IS the character entertainment...you're paying to not wait in a line & see those specific characters, guaranteed. The other part of the justification is the staff cannot "police" who is actually eating, and who is not...or how much. So everyone pays. Sorry!
Now, I would mention that Disney is very good at accomodating diet issues...even at buffets. My daughter in law was having severe dietary issues a couple of years ago (where they were eliminating about a dozen possible causes and slowly adding them back in.) While we were at Disney, she could not have dairy, gluten, soy, corn, citrus, peanuts, or eggs. We went to 2 different buffets, and both places I noted dietary restrictions...a chef came out, walked her through the buffet pointing out foods she could eat (were only a couple that were OK for her) THEN the chef started telling her all the things they could make fresh for her, making sure none of the eliminated foods were in the preparations. She ended up having 2 full plates of totally OK food. So, that is also a possibility for you...note dietary restrictions on your reservation and the girls may still be able to get foods they will eat, so it wouldn't be a total waste for you.
