2 Red Orphingtons.....squishy bellies and very ill

In the past 3 months, I have lost 2 year and a half year old red orphingtons. I first noticed their combs were "pink" not red and slumped over. Within days, their bellies became enlarged and soft. I checkd both of them to see if they were egg bound and neither of them were. Their stool was foul smelling and green and they didn't move about the coop much. I made sure they were eating and drinking, but I would have to take them aside and sit with them individually to make them as I think they weren't able to do it themselves. Has this happened to anyone? Any input would be greatly appreciated.