Remove giblets and necks from ducks; reserve for another use, if desired. Rinse ducks thoroughly under cold water, and pat dry with paper towels. Sprinkle cavities and skin with salt and pepper; fill cavities with shallots and next 3 ingredients. Prick skin with a meat fork. Tie ends of legs together with string; tuck wingtips under.
Place ducks, breast side up, on a lightly greased rack in a broiler pan. Fill pan with hot water to depth of 1/2 inch. Bake, uncovered, at 450° for 45 minutes. Turn ducks over; bake 30 minutes.
Combine marmalade and brown sugar. Microwave at HIGH for 2 1/2 minutes. Turn ducks breast side up; brush with marmalade mixture. Insert a meat thermometer into thickest portion of thigh, without touching fat or bone. Bake 5 to 10 minutes or until thermometer registers 180°. Transfer ducks to a serving platter; let stand 10 minutes before serving. Garnish, if desired.