My first suggestion is to separate them. Ball pythons are not social animals and there is no benefit to keeping them together other than "saving money". They will be much happier snakes if they each have their own house.

I am not sure what you are using to measure temps or control your heat source but you need a reptile thermostat to regulate the under tank heater and you need digital thermometers with probes to accurately measure temperatures. Dial, gauge, or stick on thermometers are not accurate.

Cork hides don't sound like a very good idea to me. Cork seems like it would be hard to clean and would grow bacteria quickly.

Your cool side should be around 80* but 78 isn't so bad. They will thermoregulate as needed, no need to worry where they are in the enclosure. That is why you have a hot side and a cool side, so they can choose.