Fill very large pot with 30 cups water and place over medium high heat. Wash meat and poultry (ingredients 1-4) and add to pot. Wash carrots, parsnip, leek and celery stalk; chop and add to pot. Make sure water covers ingredients. Cook 2 hours.
While meats and vegetables are cooking, prepare meat mixture for meatballs and filling pasta shells. Mix garlic and chopped parsley in a bowl. Soak breadcrumbs in milk, egg, salt and pepper, mix well. Add ground beef and ground pork. Divide the mixture into two parts - one for meatballs and one to fill pasta shells. Make meatballs with half of the mixture, using flour on your hands to avoid sticking. If you do not wish to pipe the pasta shells with remaining mixture, make the additional mixture into meatballs.
When meats and vegetables have cooked for two hours, add meatballs, sausages and potatoes to pot and continue cooking on medium high for 30 minutes.
Using a pastry bag, pipe the remaining meat mixture into the pasta shells. Lightly dust with flour to avoid sticking.
Thirty minutes after adding the items in Step 3 to the pot, turn off the heat and strain the broth into another pot. Heat the pot with the broth to a boil and add the stuffed pasta shells. Cook about 20 minutes or until meat is cooked through and shells are tender but firm.
Serve the soup and pasta shells in individual servings bowls. Serve the meatballs, sausages, potatoes, etc., from the pot on a serving platter for sharing.