Hi, Kimberly!
Getting to the cruise port terminal from the airport or from a Walt Disney World (WDW) resort takes just a little pre-planning in terms of logistics and to calculate the best "deal" for your family!
Ground Transportation purchased through Disney Cruise Line (DCL) has its advantages -- including baggage handling and simply knowing that you don't have to worry about traffic or arrival time. DCL is going to guarantee that you don't miss embarkation! However, at $70 per person (round trip) and with six people in my family, it just isn't a cost efficient method of transportation for us.
With a rental car, you do have the advantage of leaving when you would like and storing your belongings in the rental -- should you want to make a side trip or want to stop for supplies on the way to the port. Yet, I would investigate turning in your car at the port to avoid paying for the days you're at sea plus the parking at the port. Most rental car companies will give you this option.
The transportation option which we have found most convenient (and cost efficient) for us is to hire a private driver. We have used Bish (321-228-5990) from Golden Touch Limousine Service, and his cars are clean and comfortable. All I do is give him my travel details, and he and I work out when and where he'll meet us for each leg of our journey. I've even asked him if he would have a few snacks for the kids in the car so that we don't have to waste travel time and can avoid meltdowns.
Of course, different folks like to book the various methods to best suit their needs and budget, but I hope I've helped give you a few options to think about for you and your group. Let me know if you need more navigation.
Have a wonderful day and a magical vacation. Bon voyage!
Andi