Rinse the shrimp shells in cold water. Heat broth and reserved shrimp shells in a large saucepan over medium-high heat. Cover and simmer for 15 minutes. Discard shells. Keep the broth at a simmer over medium-low heat.
Heat 2 tablespoons of the oil in a saucepan over medium heat. Add shallots and cook until translucent, about 4 minutes. Stir in rice and cook until each grain is coated in oil and become translucent, about 3 minutes.
Add the tomatoes and wine to the rice. Cook, stirring, until the wine has completely absorbed. Using a ladle, add 3/4 cup of hot broth to the rice. Continue to stir until the rice has absorbed most of the liquid. One mixture is thick enough to leave a clear wake behind the spoon when stirring, add another 3/4 cup broth. Continue adding broth in this manner, stirring constantly, until all the broth has been used, the grains are al dente in the center and suspended in a liquid that resembles heavy cream, about 18 minutes.
Meanwhile, about 10 minutes after the risotto begins to cook, prepare the shrimp and scallops. In a large skillet, heat the remaining tablespoon of oil. Add garlic clove and cook until lightly browned. Discard garlic. Add the shrimp and the scallops and cook until heated through. Shrimp should be pink and scallops lightly browned on both sides, about 4 minutes. Transfer shrimp and scallops to a plate and cover with foil.
Pour the remaining contents of the skillet (flavorful oil included) into the risotto, and mix well. Stir in butter and most of parsley. Combine until butter melts. Remove from heat and season with salt and pepper.
Serve immediately topped with seafood and garnished with parsley.