1st Image -
Its a pain with all the rig handles between the 2 models being the same color... When they are intertwined its an absolute mad house!
2nd & 3rd Images -
The scene itself is very basic. As with most scene anything not on camera is cut out to save memory. The actual sand itself on the characters are the memory suckers on theses beach renders.
4th & 5th Images -
While the scene was rather basic the issue was the lighting. In the 4th image you can see the rock formations aren't matching up with the simulated water foam. They were blocking light from reaching the subjects faces. Its quite common for me to do this in a lot of scenes. One of the rocks that wasn't on camera is still left in because it does have an impact on the scene. It's there to block some of the hdri lighting or to be a reflection in the water.