My cockitiels are nesting?

Ok its just a matter of a week and my cockitiel eggs might hatch if everything went well.Here is the problem .When I suspected might be eggs coming my happy self was flat broke couldnt afford a nesting box.SO I took a small card board box , Put it in the cage .It isnt optimum size .I bought a nesting box as soon as i could ..well they perfer the card board box .I tried once to transfer the eggs to the nesting box and the mom and dad refuse to lay on the eggs ..so i transferred them back to the cardboard box , they went back to nesting.the cardboard box is small ..how and when can i get the family into the nesting box?Or just leave the family be? thank you