How to join all the players to the same room in photon Unity Offline Mode?

I have designed a multiplayer game in Unity 3D using Photon Unity Network plugin for multiplayer gaming. It is working fine in the online mode. I want the same multiplayer game running offline without the Photon cloud. I want all the players to join to the same room. But when I run the code below I can see only my player but not any other player.

 void Start () {
 
         spawnSpots =GameObject.FindObjectsOfType<SpawnSopt>();
         Connect ();
         //PhotonNetwork.CreateRoom("my");
         PhotonNetwork.JoinRoom("my");
         SpawnMyPlayer();
     }
 
 void SpawnMyPlayer(){
 
         if (spawnSpots == null) {
             Debug.Log("No SpawnSpots Found");
             return;
         }
 
         SpawnSopt mySpawnSpot = spawnSpots[Random.Range(0,spawnSpots.Length)];
 
         GameObject myPlayerGO = (GameObject) PhotonNetwork.Instantiate ("PlayerController", mySpawnSpot.transform.position, mySpawnSpot.transform.rotation, 0);
         ((MonoBehaviour)myPlayerGO.GetComponent ("ThirdPersonController")).enabled = true;
         ((MonoBehaviour)myPlayerGO.GetComponent ("ThirdPersonCamera")).enabled = true;
 
     }

I am trying to join all the players to the same exact room. But why it is not happening?

Please note that I am talking about Photon offline mode and I don't want to make my game single player. I want an offline multiplayer game.

Thanks in advance.