Okay, Opa . . . who is that Gary Cooper look-alike??!
Get those golf balls & fake eggs in the boxes, Brandywine. Whenever you get a chance, push a pullet in there on top of them.
The nest that's been used the last few years in my coop is 18 inches above the floor. It seems to take them quite awhile to realize that it's there for the purpose of laying eggs.
It is a good thing to have 1 or 2 of your birds using the nestboxes and they should encourage the others to "follow suite."
Any nest they build on the ground should be messed up. If there's a location that is just too inviting but inappropriate, maybe you can put something there so they can't get to it for awhile. I've used a roll of chicken wire crammed into a favorite spot like that. After awhile, they find a better place (nestbox) and lose interest in the wrong spot.
Steve