Brown onions and garlic in hot oil. Add remaining ingredients, except shrimp, crabs and spaghetti. Bring to boil and simmer 30 minutes, stirring constantly. Remove outer shell and legs from crabs, leaving meat in bottom part; break in half. Add shrimp and crabs to sauce, simmer additional 30 minutes. Add uncooked spaghetti to sauce, stir constantly until done and pour sauce over cooked spaghetti.