I must admit that while I have a long-standing dislike of MIA, on our last cruise we flew in and out of MIA and it was actually pretty decent. No lines, the staff was less offensive than usual, and the planes were on-time. We only got shuffled from one gate to another 3 times, and those gates were next to each other. So all and all, not bad.
FLL is a more pleasant airport, but it is more expensive for the transfers to Dodge Island than it is from MIA. 5 people and their luggage may be a strain for even two taxis. I'd really recommend a shuttle, such as Top Shuttle which I already recommended. A nice full-size van and they pull an enclosed luggage trailer so you aren't crammed in the van with the suitcases. They also charge a flat rate for the van, and will be there when you return from the cruise. No need to fight over taxis or stand in a line.