Over at KoOlina where the Disney resort is, there a “secret lagoon” by Paradise Cove, you will almost always see turtles there, the snorkeling can be good depending on weather but you don't need to snorkel to see the turtles. This goes without saying but do not touch the turtles!
The walking path at the lagoons is very nice (the lagoons are swimable) and agree with the suggestion for Monkeypod or Roys although neither have a view.
House without a Key at the Halekulani in Waikiki is nice for a sunset mai tai and music.
If you plan to dine off the ship, make reservations before you leave home!