I'm really no help but for what it's worth, I stayed at the RIU in June and it's adjacent to the dunn's river sandals, those are the only 2 resorts in that stretch of beach. The 2 are separated by a rock wall and Sandal's beach is small but still beautiful. It makes sense that you said it is adults only, I didn't know that at the time, but it sounded like they we're having a rocking good time, lol. This restaurant at the RIU (plantation) is next to the dividing wall and there was good music playing on the other side and people sounded like it was so much fun, we wanted to look, lol.
I also remember seeing a lot of people on the balconies at Sandals eating breakfast in the morning....that's a nice touch. If you look at my siggy pic Sandals is to the right - the water is gorgeous. I'll see if I have any pics of Sandals in my album. I hope another Sandals bride pops up for ya!