Hi,Do the chickens have their own coop? And do you have nest boxes for them? Using fake eggs in nest boxes will help them learn where you want them to lay. https://www.amazon.com/Happy-Hen-Treats-Ceramic-Brown/dp/B00GGCBD2U?ref_=fsclp_pl_dp_1
The chickens are probably attracted to the duck nests because the hens feel if it's safe for the ducks, it must be safe for chickens. Try your best to lure your chickens to lay in their own space.
Yes they have their own coop, and I have 6 nesting boxes, I did put a egg in one of the boxes, but not working.