Both the lines you mention are reputable and I'm sure they'd enjoy either one. Have they cruised before? If so, you may want to know if they prefer shore excursions? This answer may help narrow your search. Are they all of good health where they would be willing to do more 'active' excursions or of mild health where they would likely need to 'ride and watch'? Again, this may help direct the types of things you would/not plan for them.

Not too long ago 4 generations of my family took a cruise and it was quite difficult for us to find activities we would all do together (for some reason what a 98 year old want's/willing to do doesn't match what an 15 year old wants to do). Since they are not too far apart in age, you may have a 'easy' time planning. My family loves to cruise and with all the activities both on and off the ship, I'm sure you'll plan a great trip for them.