Hi Tonya,
I love that you are going to bring your grandchildren to the Walt Disney World Resort for vacation. My children have such great memories of visiting the parks with their grandparents that I am thankful they had the opportunity to experience this magical place together.
While you may see it as punishing you, I see it as being kind during the most magical time of the year. While everyone who dines with a large party is used to having the gratuity automatically added, I have rarely experienced poor service because of it. When I did experience poor service, I usually gave the benefit of the doubt to the server that he or she was having a bad day. I am also confident that somewhere they might have been shorted by the party of two and that is why my service was not stellar.
If however you feel strongly that the server on your individual meal was not deserving of the 18%, I would ask to speak to the manager. Explain to the manager why you feel that the 18% was not warranted and see if an adjustment can be made. Even if they say no, at least you asked and you provided the manager some valuable feedback about this cast member. Perhaps the cast member did not even realize his or her service was not totally Disney:)
Wishing you a magical vacation!
Beth