Brown both sausages in a large pot over medium-high heat about 10 minutes, breaking into small pieces, until deeply caramelized. Remove; set aside.
In same pot, sauté onion about 5 minutes, until softened. Cook garlic 1 minute. Return sausage; add crushed tomatoes, tomato paste, basil, oregano, sugar, salt, and pepper. Simmer 20 minutes.
Preheat oven to 375°F. Mix ricotta, eggs, parsley, 1 cup mozzarella, and 1/2 cup Parmesan in a bowl.
Spread 2 cups meat sauce in a 9x13 inch baking dish. Layer 4 noodles, half the ricotta mixture, 2 cups sauce, and 1 1/2 cups mozzarella. Repeat once.
Top with remaining 4 noodles, sauce, mozzarella, and Parmesan.
Cover tightly with foil; bake 50 minutes. Uncover; bake 15 minutes more, until cheese is golden and bubbly.
Stand 15 minutes before cutting and serving.