The meal is quite pricey for 4 (if $170x2). I wonder if it would make more sense for a group of 4 to go to Ivan's (Catcha Falling Star) or another establishment for a memorable meal that would not cost over $300.
We are at CSA right now and have noticed private dinners for 4 on several evenings. Have never seen this in previous years but have seen at least four dinners where there were two couples at the table this trip.
We saw a foursome having a beach dinner at CSA this past trip. That being said, if it were me, I'd save the private dinner for when I was just two and take a group of four for a fabulous sunset dinner on the cliff's at Ivan's if you are staying at either of the Negril properties.
You certainly may have a private dinner for 4! We went to CN last Oct. with my sister and brother-in-law and the 4 of us had an awesome private dinner in the treehouse. You also don't have to all agree on one of the two " dinner" options they give you. Each person may select which one they prefer. It is an experience not to be missed! We have done it 2 years in a row and are contemplating doing another one on our next visit. Lots of wonderful memories were made!