Could they have gotten bitten by something, snake, or poisonous bug, spider? Could they aha eaten something poisonous? Check your food to make sure it isn’t moldy. It could be smoke, and how hot is it were you are? Do you still have the bodies? If so, you could keep them cold, not frozen, and send them to a state lab of testing. I don’t know much about that, but @Eggcessive does. I hope you figure out what it is! Avery