Hi Emma,
Wow! What a fantastic vacation you are planning. Celebrating milestone birthdays at Walt Disney World with a large group will create memories that will last a lifetime.
First, do be sure to pick up free Happy Birthday buttons for your parents to wear on their birthdays. It is so much fun to hear cast members and other guests alike offering celebratory greetings all day long! Sometimes when wearing a birthday button, a guest may receive a little extra pixie dust, like a birthday cupcake. This is not guaranteed, so please do not expect anything other than birthday greetings!
For an enjoyable activity for your whole family, how about a
specialty cruise? There are different types of specialty cruises, from cruises that include fireworks viewing to renting the luxurious Grand 1 Yacht. Due to the size of your party, you may have to split your party into two boats for some of the cruises. I have done this in the past, and it is still a great time. For a cruise on which we viewed Illuminations, we had a large party spread over many boats. The cast members were able to stop the boats right next to each other while we viewed the nighttime spectacular.
If you are looking for something special for your parents to do together, perhaps booking a lovely meal for them would make lasting memories. One of my favorite places for an elegant dinner out is Disney's Grand Floridian Resort & Spa, with restaurants such as Citricos and Narcoossee's. For the ultimate evening out, there is also the fabulous Victoria & Albert's.
No matter what you choose, I am sure that you will create lasting memories for your parents and your whole family. Have a wonderful time planning your vacation, Emma, and please do not hesitate to ask if you have any further questions.