DO also be aware if you do not book with the ship and you are late to return to the ship when it's time to leave port, they will NOT wait for you and you are responsible to get yourself back on board. IF you book with the ship, they will wait.
That being said, we have never booked an excursion through the cruiseline, but there is just the two of us and we know we will make it back on time come hell or high water. You know your family and your group. Some see the extra money spent booking excursions through the ship to be cheap insurance so they aren't left behind. This is an especially important consideriong if your excursion takes you far from the port. Vans/trucks break down every day. I don't want to scare you, but you do need to be aware of this part of the deal when you book independently. Like I said, we have ALWAYS booked independently. But you know your group, what excursions you might want to go on, and your stress level....
One of our favorite things to do as the ship is pulling away from port is watching the pier runners frantically trying to make it back on board. Priceless!!!