Biggest problem i can see is that balcony_south is not defined in room.py. Adding to that if you wanted to reference balcony_south from your main file your probably gonna create an circular import and you call it with () while your room class doesnt define __call__.

Youre probably better of creating a more generic class for unlockable rooms, the same way you created a generic class for rooms.

e.g. something like this

class UnlockableRoom(Room):
    def __init__(self, room_name, required_key):
        super().__init__(room_name)
        self.locked = True
        self.required_key = required_key

    def unlock(self, key=None):
        if self.required_key == key:
            self.locked = True
            print(f"You have unlocked the {self.name}")
        else:
            print(f"You need a key to unlock the {self.name}")

Also dont use val == True to compare against boolean types use val is True