I was stunned when all three used the boxes.I put one in each location I want them to consider laying in, lol. Knowing my girls though they'll lay wherever they want and I'll be fishing eggs out from under the hen house, rather than in the boxes.
When one goes on the nest, one or both of the others follow them into the coop and croon at the nester. (The second generally stands guard duty at the coop door, braying at anyone in eyesight.) Slightly clumsy midwives/doulas, but enthusiastic.
I got them at 7 1/2 weeks. They might have had a little broody rearing, but not much. Bird instincts are utterly amazing.