There are 2 resorts on St. Lucia, 1 resort on Antigua, and 1 resort on Turks and Caicos (T&C) to take a look at. I will note what is all-inclusive pricing and what isn't. I also picked ones that aren't just hotels, have some activities included in the final price, are generally different than what you will find on the rest of the island, but also aren't big commercial brands (Sandals does have properties on St. Lucia and Antigua).
The vibe on these islands are going to be different than Mexico. On the resorts there isn't too much of a nightlife. There will be a bar, and maybe some live music on some nights, but it will be relatively quiet.
ST. LUCIA: English-speaking, and French-Creole. Mountainous island that can take time to maneuver in a vehicle due to the hills and curves. Very green and tropical. St. Lucia is shaped like an egg. The international airport is at the very South of the island. Most of the resorts are at the north, so the ride to the resort and back to the airport can take about 1.5 hours depending on traffic.
Calabash Cove: built up on a cliff with a small beach (dark sand). One main restaurant. Gourmet chef. One pool. Very boutique, cute property. Great for disconnecting! All-inclusive pricing: For an oceanview room (first picture is an example of the view) estimate: 6745.52. Swim-up Junior Suite (3rd picture where you step off your patio into the pool) estimate: $7309.52. This pricing is 45% off right now!
Anse Chastanet: All rooms here are built UP into the hillside, so there is a lot of privacy. The rooms are very airy, but have AC. There is a possibility that you could have an open shower (last picture). This resort is one that was featured on The Bachelor series during the red rose proposal. Truly a different property with two beaches. It stays pretty quiet here as well, but there is plenty of options for activities and several restaurant options (APSARA is not included in the AI pricing). Customer service is amazing and the food is great. They have a chocolate farm on property that you can tour. A beachside deluxe all-inclusive with the 3rd night free estimate: $6843.52. Beachside Deluxe breakfast and dinner daily with the 3rd night free: $6067.52 (on own for lunch and all drinks).
ANTIGUA: Technically, it is Antigua and Barbuda: 2 islands and several smaller ones forming "one" large island. Antigua is generally flat with some cliffs, rolling hills, and rainforest. This is good island to rent a car for a day or two and run around the island. English-speaking, but you will hear a patois, like Jamaica.
Galley Bay: One of my favorites because of the layout. See map below. Almost all of the rooms are beachfront. Very easy to get around. Live music is almost nightly here. Great beach. There are two rooms that are very similar to each other for you both: Superior Beachfront is the smallest and the size of a typical hotel room. Deluxe gives a little more living space. Deluxe Beachfront estimate: $5830.52. Deluxe Beachfront: $6130.52
TURKS AND CAICOS: This is small island with beautiful water. It can be easily gotten around in via taxi. Or there are bicycle rentals available to get around town. Antigua and T&C have very clear water for snorkeling, fishing, and if you would want to try scuba. A good island to go into downtown and enjoy the nightlife.
Alexandra Resort: Sits on Grace Bay - best beach in T&C. You would be within walking distance of several restaurants or a short taxi ride. Or bicycle! Alexandra is sister to Blu Haven and Beach House hotels, so you do have the option to use their restaurants for dinner and to use the beach at Beach House. Blue Haven's beach is very small, but right next to the marina. These are essentially condos, so if you didn't want to do AI and not eat out at all meals there is the opportunity to keep breakfast food on hand or small lunch meals. Studio Oceanview (example of the view in 2nd pic) estimate: $4457.52 - no meals. Studio Oceanview all meals and alcohol at lunch and dinner estimate: $6612.52