They'll usually go off food if not kept warm enough. I wouldn't recommend the heat mat on the side, they don't really work well this way for horned frogs because the frog would rather burrow in the soil during the day than surface to get heated. They're actually more effective on the bottom and despite the claims of others, they are perfectly safe used this way if thermostat-controlled and set up correctly. I would say heat from above with a ceramic heat emitter but you have 8 and this may be a bit of hassle. Heating the room with a oil filled radiator would be a good choice, if possible. Also, misting 3 times a day is excessive because they don't need that high of humidity, a good rule is to keep the substrate on the moist side, but not wet