Preheat oven to 350°F. Coat a 13- x 9-inch baking dish with cooking spray. Cook sage ground sausage and hot ground sausage in a large skillet over medium-high, stirring often, until they are crumbled and browned, about 10 minutes. Remove from heat; drain well on paper towels.

Working in batches, cook hash browns in a large nonstick skillet according to package directions; omit salt if called for on package. Sprinkle with 1 teaspoon of the salt and 1⁄2 teaspoon of the pepper.

Stir together sausage, hash browns, and 1 cup of the cheese in a bowl. Spoon into prepared baking dish. Whisk together eggs, milk, and remaining 1 teaspoon salt and 1⁄2 teaspoon pepper in a medium bowl. Pour over sausage mixture. Sprinkle with remaining 1⁄2 cup cheese. Bake in preheated oven until set, about 30 minutes. Sprinkle with parsley and chives.