Do I read this right and you are ONLY feeding them scratch and corn and not a preparatory feed.... ie pellets or crumbles?? If so, you are setting them up for a lot of health problems and possible early death. I'm afraid you need to be much more disciplined with them about food. You are letting them dictate to you what they eat. The longer you allow it to continue, the harder it will be to break. What did you feed them as chicks? Perhaps start by going back to that, but you need to stop feeding them corn and scratch before the damage is irreversible. Fat chickens are no more healthy than fat children or dogs or any other creature and corn makes them fat. Cut out everything except a preparatory feed. They can live off their body stores for several days, especially if they have the fat reserves chickens fed solely on grains will have. Mix a little scrambled egg with some pellets/crumbles soaked in water. Initially start with scrambled egg and once they are eating it, gradually add a little more of the feed/water mash. It may take a while to get them onto dry pellets or crumbles but you need to persevere.