Awww, that is just so ridiculous, esp if these people have been to Disneyland and watch the movies! These are small children, and I think even they could see the hypocrisy of their parents!
I really hope you can get enough kids to come so your little girl won't be disappointed. This bunch sounds like some judgemental a**holes, trying to look pious in front of each other. What onearth is magical about a princess party? Every little girl wants to be a princess.
You have been given some sound advice here, I can't add much except to say I hope after you are done with the cult book, you will find a way to get your wife and daughter out. Just go slowly so you don't scare her!