I not to sure about whether you should replace their made nest with a nesting box but I do know about how to test you eggs. All you do is get a bowl or glass with water in it deep enough to cover 2 eggs end for end on top of eachother, vertically. Then grab one egg and using your hand in the water release the egg at the bottom of the container, if it floats it is not good to use but if their is no gap between the egg and the bottom of the container (where you released it) that they should be fine. But when cooking be sure to check that the eggs you think are alright are before you use them. Hope you can follow my intructions and aren't too confused.