The way gliders die can be somewhat informative. I asked a breeder/rescue worker friend that I have. Their response was dehydration/seizures most likely given the location and that they were still clinging to fabric. Have you checked their water bottle to make sure that it wasn't clogged? If they were stuck for a few hours, they wouldn't die. They would chew off a hand or finger. Unless they were stuck there for an extended period of time, their nails were most likely not a direct cause. I would go with a nutritional deficiency, maybe, based on the description of their diet. Even with water available gliders can suffer from dehydration, coupled with a poor diet, it's possible their body was overworked and they had organ failure.