Some of my best and sweetest babies have been the runt of the clutch. Nature knows best. Not all eggs are meant to hatch. Obviously if none of your eggs are ever hatching, you should be concerned. Believe me, in nature all the eggs do not hatch every time.
Splay legs can be very traumatic for the novice breeder.
Even the best nest-builders should be given a basic substrate for the nest box. I recommend Care Fresh. It is nontoxic and easy to get. Put about 2-3 inches into the nest box. Then give the hen nest-building materials.