There are a number of accommodations in Barahona that will fit your group's needs.
Hotel Costa Larimar is located in the town of Barahona and about 15 miles (40 minutes) from Batey 7. It is easy walking distance to most things you might need. Rooms are clean, comfortable and air conditioned. Food is great and they can accommodate large groups. It is located on the bay side and has beautiful sunrise and sunsets. You can have a meal plan included with your stay. It is served buffet style and is very good. The dinning area is open air as it is in most of Barahona.
Cell phone service with AT&T, Verizon and T-Mobile are pretty good. Make sure you have the international plan and data package if you are going to be making phone calls thought. There is WI-FI at the hotel although as with many things in the Dominican Republic it may not work all the time. Photos of the hotel are below.