Begin by poaching the whole crabs: To prepare the crabs, set a large pot of cold water with the garlic, bay leaves, black peppercorns, kosher salt and chili flakes over high heat. Bring to a boil, and then drop in the crabs. Once the water starts to boil again, reduce the heat and simmer for 12 to15 minutes. When the crabs are done, shock them in cold water so they stop cooking. Then break each one into 4 pieces, with the pieces cracked to let the sauce in.
For the cioppino: In a large stockpot over medium heat, heat the oil and cook the onions, fennel and bell peppers until lightly browned. Add the minced garlic and tomato paste and cook until it browns, stirring often. Add the tomato sauce, 4 cups water, wine, clam juice, lemon juice, sambuca, half the parsley, the chili flakes, salt, basil, oregano, pepper and bay leaves, and simmer for 1 hour.
Add the pieces of cooked crab to the sauce and simmer for 20 minutes. Add the clams and simmer for 5 minutes. Add the fish and shrimp and cook until the shrimp turn pink, 4 to 5 minutes. DO NOT STIR. Remove the bay leaves, stir in the remaining chopped parsley and serve immediately with bread.