Hi Michele,
The Extreme Getaway Package on Castaway Cay is a great idea and your boys will have a really good time! It's an awesome price for everything that's included, and you'll have enough time to do it all. I love Castaway Cay. Your kids are welcome to bring their own masks and snorkels if they wish. Castaway Cay is gorgeous, and if Disney offered a cruise that docked there for a week, I'd gladly book it, and happily not sail anywhere else.
You won't have to pay extra for lunch.
Cookies BBQ and Cookies Too are great outdoor restaurants that serve buffet style. It's all you can eat and includes barbecue, fish, flatbreads, salads, chicken and fish. There is a fresh fruit bar and soft serve ice cream close to the Cookies BBQ location. The food is great, so don't miss out!
Please let me know if you have any other questions. Thanks for visiting the Moms Panel. Bon voyage Michele!