I have never heard of doing this with water fowl only chickens since they are kind of i n a trance when they sleep it works sometimes but with water fowl they never fully are asleep from all I have read so I think introducing them with fencing between them is best that way they can live side by side while littles are growing and then when littles are same size as adults they will be ready to be 1 flock.What do you mean by introducing "them at night"? Put them all in the same house together for the night?? Wouldn't they all kill each other?
Lol