You should have no problem finding taxis. Follow the signs in the airport (or ask someone, if you don't see them) to the designated taxi stands outside the terminal. The line moves quickly and is kept orderly by the dispatcher. Sometimes, you can request a van from the dispatcher, but that may entail a wait and an additional charge of, I think, $5.
We've done 3 in a taxi with luggage with no problem. It's a short trip, maybe 10 minutes. Cost should be about $20-$25 per taxi, which includes a roughly $8 fee imposed by a number of authorities.
A couple of things to be aware of: Taxis are metered - do not pay a flat rate to go to the cruise terminal. Also, make sure the fee is entered onto the meter before you leave the airport. Some drivers pocket it, otherwise. The best way around this is to pay by credit card.
I'll check into shuttle companies, but I don't know of any other than those offered through the cruise lines (which charge per person). I'm quite sure your party can do this in 3 taxis. There's also a public transportation option, but you'd need to carry your own luggage and make a transfer. I recommend a taxi (or 3) as the best option.