I give my corn, sunflower seeds, porridge, kitchen veg scrapps
but i also made scrambled egg with corn sunflower seed and i put some egg shell in crumbles and put in for them they love it
If I was you in my nesting box I have straw and sawdust i put a yellow gold ball in my too so the look Like another chicken has already layer there egg the so they think it is a safe place to lay there egg too. Perhaps put it I closed so they are feeling secure when laying