Cut through the top of the lobster shells down the center, just to the tails, using kitchen shears. Split the shells. Use thumbs and fingers to spread open. Gently loosen lobster meat; pull meat away from bottom, leaving shells empty. Reserve shells. Rough chop lobster and set aside.

For sauce, combine limoncello and lemon juice in a small saucepan; warm over medium-low heat. Whisk in butter; cook over low heat for 2 to 3 minutes or until bubbly. Remove saucepan from heat; whisk in heavy cream.

Stir together panko and 2 tablespoons limoncello sauce in a small skillet. Heat panko mixture over medium heat until lightly toasted, stirring occasionally. Set aside.

Set aside ½ cup limoncello sauce for serving. Leave 4 shrimp whole and set aside. Discard tails on remaining 8 shrimp; chop. Add lobster and chopped shrimp to the remaining limoncello sauce in saucepan. Heat over medium heat for 2 to 3 minutes or until heated through (145°). Remove from heat; stir in celery and 2 tablespoons chopped chives.

Spoon seafood mixture evenly among lobster shells. Place on a serving platter. Top with toasted panko mixture and whole shrimp. Serve with reserved ½ cup limoncello sauce, and garnish with additional fresh chives, dill, and grilled lemon slices, if desired.