Clarity-
Catcha IMO is the most romantic place I have ever been or seen. I think it would be everything your parents would need, but you are right, the only real down side I would see would be for your father getting in/out of the water.
Plus there are no vendors at all while on the cliff properties, so that is not even a concern.
But if they do happen to pick a beach location I would recommend that they have their anniversary dinner at Ivans (Catcha), call ahead and speak to Andrea or Mauvette and I bet they would do something really nice for them, be sure they go for the sunset too!
Either way, I just know they will have a wonderful trip!
Yeah it's a tough life having SO MANY great choices and options, right?