The duck house is beautiful.
You'll have to herd the ducks in until they form the habit of going inside at night. It is often easier if you use some sort of low fencing to funnel them into the doorway.
Somehow, my ducks formed the habit of my putting them to bed at night. So they stand around outside their run until I walk out there and announce it is bed time. Then they go in.
On the nights when I am really late, they will finally put themselves inside, but I really hear about it when I go out to close the door. Nobody can scold like a duck and ducks don't like to have their routine changed.