I found cutting a sheet (rag etc.) and hanging it over the nest box opening helps "train" them when I move them etc. I only partially cover the opening. It improves the perception of privacy by darkening the box, and partially closing it off.
When they get laying them around the house, they are preferring locations in the house over the nest boxes you have provided. They instinctively nest on the ground in the darkest locations where they feel more private. Behind the door etc., and often in the corners. By hanging the rang over the opening of the nest boxes, the nest boxes become the darkest, most "secure" locations in the house.
Do not completely cover them, and leave an egg or fake egg in them, and see if it changes their habits. There will always be the exceptions, but I think that you will find that it works.
I leave a gap at the edges, bottom, and middle.
I can't see chipping the birds as a practical option. They spend too much time entering nest boxes for reasons other than laying eggs.