What cruise line do you suggest for 2 active upper 50 year olds going to the Caribbean with their two late 20's aged adventurous daughters and two active grandchildren aged 7?

RCCL & Carnival

I agree with Eschew. I do like RCCL (now called RCI) a bit better than Carnival. I have been on both several times.

For the Caribbean, I also think Princess would be fine. The crowd on Princess in the Caribbean was younger than on other Princess cruises, so you don't have to worry about ages. After you pick your cruise (no matter which one), join cruisecritic's roll call for your ship, and join up with others for some great shore excursions and adventures. Lots to do in the Caribbean and on the ship.

I would choose the cruise line that has the best stops or the stops you particularly want to see or the number of days at sea, etc. I have been on several cruises on RCL and Carnival and each of them offer as much or as little as you would like to do while at sea.
I would imagine all cruise lines offer the same choices for the most part of the shore excursions so I would not factor that into a decision.

If t was me I would choose RC over Carnival. Did both and both were okay, but RC was just a notch or 2 better. Better food, service, just as much fun for young and older adults, ships are better, newer, more sophisticated, etc.

That said, Norwegian is suppose to be okay (don't know, never tried the line), Holland is a retired persons vacation special but can't confirm that either, but surprisingly Disney is becoming very popular with adults when not in season with hundreds of children running around.

Celebrity is more upscale, refined but not as fun as RC or Carnival.

There are probably couple more but I can't think of them now.

Good luck with your choice and have a wonderful cruise!

Never ever go on Holland America.. Services, food are horrible, and entertainment are boring

Our favorite is Princess, it has something for every age group and great food and service.

I wouldn't call HAL "horrible and boring" but it does cater to an older crowd.