Tjos os NOT a definitive diagnosis, but general swelling with hemorraghic lesions (red spots on the body or shell) often indicate bacterial sepsis. It is unlikeky that two turtles would die simultaneously , even if both were infected. Here is one possible cause (this happened to me years ago): if you have an undergravel filter, it sets up a specific bacterial flora in the gravel BUT..,. if the filter shuts down for even a brief time, you can get a rapid overgrowth of anaerobic bacteria in the accumulated waste, including the deadly Botulina bactera that can rapidly cause total parlysis and death from repiratory failure and drowning. The turtle ingest it while feeding on the bottom. Is this a possibility?? (sorry for the typos, but my format is screwing up and I can't retype).