Pour 1 gallon of water into a lobster pot or stockpot large enough to hold all ingredients. Add potatoes and salt and bring to a boil. Cook, covered, 10 minutes (potatoes will be slightly softened but not cooked through).
Put coriander, fennel, thyme, and peppercorns in a large piece of cheesecloth. Gather edges together and tie with kitchen string to make a pouch.
Add spice pouch, wine, chorizo, and lobsters to pot with potatoes. Boil, covered, 5 minutes. Add clams and corn and cook, covered, until lobsters are cooked and clams have opened, about 5 minutes (discard any unopened clams).
Cut each lobster in half using a heavy knife and kitchen shears. Serve each person half a lobster, 6 clams, half an ear of corn, 2 potatoes, and a piece of chorizo.