IMO the most economical and convenient course would be for you to hire a driver with a van large enough to accommodate your group to pick you up at the airport and take you directly from there to LT via the new highway. The trip using the new highway should take less than 2 hours and will get you all the way to LT. Taxis are just too expensive. The Caribe Tour will take you 4 hours leaving from the capitol and will only get you to Sanchez where you will be required to get a taxi or guagua for the remainder of the trip. Moreover, I just can't imagine how you would manage that large a group on a Caribe Tour bus. If you send me a PM I can give you a recommendation for a driver, or you can ask a number of other posters who can help you arrange for an airport pickup. Although I agree with Dolores that a rental will come in handy in Samana, if you have never driven a vehicle in the DR and have no familiarity with the landscape, it will be difficult, even with the new highway.