Place crabmeat and shrimp in a dish; coat with lemon juice, lime juice, 3 cloves garlic, 1/2 teaspoon salt, and 1/2 teaspoon black pepper. Mix well. Cover with plastic wrap; chill until ready to use.
Combine rice, 3 cups plus 2 tablespoons water, coconut milk, chopped onion, butter, 2 teaspoons salt, and 1 clove garlic in a large saucepan or rice cooker. Simmer, covered, until water is absorbed, about 15 minutes.
Heat dende oil in a large skillet over medium heat. Cook and stir sliced onion until beginning to soften, about 5 minutes. Add yellow bell pepper, orange bell pepper, and crushed pepper. Cook and stir until heated through, 3 to 5 minutes. Add sliced tomatoes, chopped tomato, and green onions. Reduce heat to low; let vegetable mixture simmer for 5 minutes. Add the remaining 1/2 teaspoon salt, 1/2 teaspoon black pepper, and cilantro.
Transfer 1/2 the vegetable mixture to a plate. Spread the remaining mixture to evenly cover the bottom of the skillet. Spread crab-shrimp mixture on top. Top with the remaining vegetable mixture and pour on coconut milk. Bring to a simmer over medium heat. Reduce heat to low. Cook without stirring until flavors blend, about 15 minutes. Serve over the rice.
