I agree with the rec's for both 50's Prime Time and Coral Reef. 50's is comfort food, with pretty consistent reviews. Plus, I think the older members of the group would enjoy the 50's nostalgia, while the little kids will be entertained by the adults getting in trouble for not eating their veggies, having their elbows on the table, etc. The food at Coral Reef plus the giant aquarium windows would make it a good choice for your family.
If you wanted to do character dining, as PP mentioned, Garden Grill at Epcot would be a good choice if your dad doesn't mind family-style service. Also, if you wanted to see princesses, Akershus at Epcot would work, as you order off the menu. There is a salad-bar type setup with salads, cheeses, salmon, etc., but the entrees are individual servings. Dessert is served family style. Cinderella's Royal Table isn't a buffet, either.