Cut off the tops of peppers. Remove ribs and seeds; rinse peppers. Chop edible portion of the tops; set aside.
Bring a large pot of salted water to a boil. Add peppers, reduce heat, and simmer until tender but still firm, about 5 minutes. Drain and set aside.
Heat butter in a medium skillet over medium heat. Sauté reserved chopped pepper, onion, and celery in hot butter until tender, 3 to 5 minutes. Stir in crushed tomatoes, tomato sauce, and garlic. Season with 1 ½ teaspoons salt, basil, oregano, and ¼ teaspoon black pepper. Simmer uncovered for 10 minutes.
Preheat the oven to 350 degrees F (175 degrees C).
Meanwhile, combine Parmesan cheese, egg, Worcestershire sauce, 1 remaining teaspoon salt, and remaining ¼ teaspoon black pepper in a large bowl. Mix in hot sausage, mild sausage, bread crumbs, and 1 cup tomato sauce mixture until well combined.
Fill each pepper with sausage mixture using a piping bag or sausage stuffer. Place in a 3-quart casserole dish; pour remaining tomato sauce mixture over peppers.
Bake uncovered in the preheated oven until sauce is bubbly and sausage is cooked through, about 1 hour.
