I'm not a vet, but I'd say, that they are just victims of old age. I suppose you might have "damaged" something if you were force-feeding them, but that's not likely, IMHO. And I'm assuming they're not defecating as they should have by now?Probably they need to be euthanized if they're not eating. Force-feeding just prolongs the inevitable. Of course there would be the slim possibillity that they're gravid? (Do you know their sex?)