Give Talk of the Town Tours a try. http://talkofthetownnegril.com/tours.htm
They have good, air conditioned vehicles and will do a good job for you and your friends.
I would (personally) think long and hard before taking a boat from Negril there as when you get past Sav the ocean gets quite rough and sometimes a boat takes a likkle longer due to the often onshore South winds. I went from Lost Beach once and it was a "bump and slam" trip that left me exhausted. I did it also from Treasure Beach (Billy's Bay) and going to Black River was nice and smooth but coming back was pretty scary!
Peace and Guidance