You don't need Disney for an Alaskan cruise. (We did Holland and thought it was great). Even if Disney is your preferred cruise line, this cruise is about celebrating with your PARENTS. Given they are paying for the trip and asked you to join them, simply say "thank you" and enjoy the trip. It doesn't matter whether you think Disney is or is not better for your family. You are a guest. To choose not to go because it isn't your preferred cruise line is petty. You are passing up the opportunity to celebrate a significant family milestone, that you and your children will carry with them for years to come.