Preheat oven to 375 degrees F. Place potatoes in separate bowls. Add half each of the cream cheese and sour cream to each bowl; season with salt and pepper. Mash with potato masher or fork until creamy.
Stir half of the Parmesan cheese into white potatoes. Stir half of the Cheddar cheese into sweet potatoes. Alternately layer half eachof the white potato and sweet potato mixture in 2-qt. clear glass casserole. Repeat layers.
Bake 15 min. Sprinkle with remaining cheeses; bake 5 more min. or until cheeses are melted.