We stay at Divi and the beach there is fine and there are always plenty of beach chairs and umbrellas available. That said, it would still be fun to see one other beach, such as Orient, where you could have a great lunch at somewhere like Kakao, or Mullet, just for the waves and view.
Unless you have some special reason to go for dinner at Oyster pond, maybe you'd want to consider dinner that evening somewhere in the Simpson Bay Area or Maho, so it would be closer to Red Piano. It's almost 30 minutes one way to Oyster Pond, so that's going to be an hour driving that night, as well as the night you to go Grand Case.
For your last night's dinner, Antoine's in Phillipsburg would be close and very good.
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