I clip one wing on my females each fall after their big molt we don't have neighbors but we are surrounded by woods and lots of predators.
They do love to fly but I want mine to live too. My drakes have never flown they like to stay put where their females are. Your ducklings are adorable...
I have many duckling and never a quack like a domestic duckling. Sometimes when I would catch one of my adult female she’d let out a quack but only one.
If there is quacking it’s not a Muscovy. They are called quackless ducks because they don’t quack they make a trilling sound and drakes when mature make a huffing sound. You can hear the noise they make by looking Muscovy up on line.