Is there anything else I could use as fake eggs, besides gold balls?
You could use anything that is approximately the size and shape of a chicken egg.
Plastic easter eggs filled with sand for weight are often used.
I keep 1-2-3 in all 4-5 nests...and remove and/or move them around sometimes just to see what happens.
You only need 1 nest for every 3-4-5 birds...I have 4 nests for 14 hens, busy days can get a little raucous.