I'm so sorry for your loss. I would also say dehydration. I don't think it would take that long for them to expire with it being so hot in the tank and no water source. I keep my temps in the mid 70's for my frogs and leave extra water bowls in all my tanks during the summer months just in case. Ventilation is good but too much can also dry them out. Don't use a heater until the fall at the earliest. Also keep an eye on how much heat your light fixture may put out. A mister is a good idea and will allow you to take a vacation and not have to worry so much about your frogs. Again, sorry to hear about your frogs. Hang in there and try again.