Melt 2 tablespoons of unsalted butter in a medium skillet over medium heat. Add minced garlic and sauté until fragrant, about 1 minute. Stir in lobster meat and crab meat, cooking until heated through, about 2-3 minutes. Set aside to cool.

Combine the sautéed seafood mixture with softened cream cheese and shredded mozzarella cheese in a mixing bowl. Season with salt and pepper to taste and mix until smooth.

Bring a large pot of salted water to a boil. Cook jumbo pasta shells according to package instructions until al dente, about 10-12 minutes. Drain and rinse under cold water, then cool.

Melt the remaining butter in the same skillet. Stir in all-purpose flour, cooking for 1 minute. Gradually whisk in heavy cream until smooth. Add Parmesan cheese and mozzarella cheese, mixing until melted and creamy.

Preheat the oven to 375°F (190°C). Spread a thin layer of cheese sauce in a baking dish. Stuff each shell with the seafood filling and place them seam-side up. Pour remaining sauce over the shells.

Cover with aluminum foil and bake for 20 minutes. Remove foil and bake for an additional 10 minutes until the top is bubbly and golden.

Let cool for 5 minutes before serving. Garnish with extra Parmesan or fresh herbs.