Preheat the oven to 325 degree F. Bring a large saucepan of salted water to a boil. Add the macaroni and cook until slightly al dente, about 10 minutes. Drain and set aside to keep warm. Whisk the eggs in a large bowl until frothy.
Add the Velveets, butter and 2 cups of the half-and-half to the large bowl of eggs. Add the warm macaroni tossing until the cheese has melted abd the mixture is smooth. Add the remaining half-and-half, 3 cups of the sharp yellow cheddar, the remaining grateed cheeses, salt and pepper, tossing until completely combined in the large bowl.
Pour the mixture into 9 x 13-inch casserole or baking dishes (approx 3 (3 qt) baking dishes and bake for 30 minutes. Sprinkle with the remaining 1 cup of sharp cheddar and bake until golden brown on top, about 30 minutes more. Serve hot.