Glass tanks are fine. But you do need other supplies.
The tank needs a secure mesh top to let air in and keep the snakes in.
You need an under tank heater (UTH) with a thermostat on one side of the tank to keep your snakes warm.
Also, water bowl, hidey holes, etc.
Also, you should consider getting another tank and separating your snakes. Corn snakes do better alone than they do together. It's possible to keep them together, but you do run the risk of them hurting each other or possibly killing each other.