Model as Prefab - lots of this prefab causing problems

Hi there!

I have a problem. I have made a Keypad/Keylock Model with GUI in WorldSpace and Script on it. I have made a prefab with this Gameobject/Model. If i use one of this prefab in the scene everything works fine. but if i use this prefab more than 1 time in the scene i get problems. because the second prefab is talking with the first prefab. if i press a button on the second prefab, the button get pressed on the first prefab and on the second prefab nothing happens! why is this so? i show you a pic of the inspector variables!

      public class Keypad : MonoBehaviour
      {
          public string correctPassword;
          private string passwordInput;
          public Door affectedDoor;
          private int numberOne;
          private int numberTwo;
          private int numberThree;
          private int numberFour;
    
          public Text numberOneText;
          public Text numberTwoText;
          public Text numberThreeText;
          public Text numberFourText;
  
          private bool numberOneAdded = false;
          private bool numberTwoAdded = false;
          private bool numberThreeAdded = false;
          private bool numberFourAdded = false;
  
          private bool keypadActive = false;
  
          public Text passwordField;
          public Camera mainCam;
          public Camera keypadCam;
  
          public MeshCollider meshCol;
          private FirstPersonController playerController;
          private GameManager_ToggleCursor toggleCursor;
  
          void Start ()
          {
              SetInitialReferences ();
          }
  
          void SetInitialReferences ()
          {
              playerController = GameObject.FindObjectOfType<FirstPersonController> ();
              toggleCursor = GameObject.FindObjectOfType<GameManager_ToggleCursor> ();
  
          }
          void Update ()
          {
              if ( Input.GetKeyDown (KeyCode.Q) )
              {
                  LeaveKeypad ();
              }
          }
  
          public void MoveCameraToKeypad()
          {
              this.mainCam.enabled = false;
              playerController.enabled = false;
              this.gameObject.layer = LayerMask.NameToLayer ("Default");
              toggleCursor.isCursorlocked = false;
              Cursor.visible = true;
              this.keypadActive = true;
              this.keypadCam.enabled = true;
              this.meshCol.enabled = false;
          }
  
          public void LeaveKeypad ()
          {
                  this.mainCam.enabled = true;
                  playerController.enabled = true;
                  toggleCursor.isCursorlocked = true;
                  Cursor.visible = false;
                  this.keypadCam.enabled = false;
                  this.meshCol.enabled = true;
  
              if (keypadActive == false)
              {
                  this.gameObject.layer = LayerMask.NameToLayer ("Default");
              }
              else
              {
                  this.gameObject.layer = LayerMask.NameToLayer ("Interactable");
              }
          }
  
          public void CountNumberOneUp ()
          {
              numberOne += 1;
              numberOneText.text = numberOne.ToString ();
  
              if(numberOne > 9 )
              {
                  numberOne = 0;
                  numberOneText.text = numberOne.ToString ();
              }
          }
  
          public void CountNumberTwoUp ()
          {
              numberTwo += 1;
              numberTwoText.text = numberTwo.ToString ();
  
              if(numberTwo > 9 )
              {
                  numberTwo = 0;
                  numberTwoText.text = numberTwo.ToString ();
              }
          }
  
          public void CountNumberThreeUp ()
          {
              numberThree += 1;
              numberThreeText.text = numberThree.ToString ();
  
              if(numberThree > 9 )
              {
                  numberThree = 0;
                  numberThreeText.text = numberThree.ToString ();
              }
          }
  
          public void CountNumberFourUp ()
          {
              numberFour += 1;
              numberFourText.text = numberFour.ToString ();
  
              if(numberFour > 9 )
              {
                  numberFour = 0;
                  numberFourText.text = numberFour.ToString ();
              }
          }        //Count numbers down
      public void CountNumberOneDown ()
      {
          numberOne -= 1;
          numberOneText.text = numberOne.ToString ();
          if ( numberOne < 0 )
          {
              numberOne = 9;
              numberOneText.text = numberOne.ToString ();
          }
      }
      public void CountNumberTwoDown ()
      {
          numberTwo -= 1;
          numberTwoText.text = numberTwo.ToString ();
          if ( numberTwo < 0 )
          {
              numberTwo = 9;
              numberTwoText.text = numberTwo.ToString ();
          }
      }
      public void CountNumberThreeDown ()
      {
          numberThree -= 1;
          numberThreeText.text = numberThree.ToString ();
          if ( numberThree < 0 )
          {
              numberThree = 9;
              numberThreeText.text = numberThree.ToString ();
          }
      }
      public void CountNumberFourDown ()
      {
          numberFour -= 1;
          numberFourText.text = numberFour.ToString ();
          if ( numberFour < 0 )
          {
              numberFour = 9;
              numberFourText.text = numberFour.ToString ();
          }
      }
      //Add numbers to the password field
      public void AddNumberOne ()
      {
          if(numberOneAdded == false )
          {
              passwordField.text = passwordInput += numberOne.ToString ();
              numberOneAdded = true;
          }
      }
      public void AddNumberTwo ()
      {
          if ( numberTwoAdded == false && numberOneAdded == true )
          {
              passwordField.text = passwordInput += numberTwo.ToString ();
              numberTwoAdded = true;
          }
      }
      public void AddNumberThree ()
      {
          if ( numberThreeAdded == false && numberTwoAdded == true && numberOneAdded == true )
          {
              passwordField.text = passwordInput += numberThree.ToString ();
              numberThreeAdded = true;
          }
      }
      public void AddNumberFour ()
      {
          if ( numberFourAdded == false && numberThreeAdded == true && numberTwoAdded == true && numberOneAdded == true )
          {
              passwordField.text = passwordInput += numberFour.ToString ();
              numberFourAdded = true;
          }
      }
      public void ResetNumbers ()
      {
          passwordInput = "";
          passwordField.text = "";
          numberOneAdded = false;
          numberTwoAdded = false;
          numberThreeAdded = false;
          numberFourAdded = false;
      }
      public void CheckIfPasswordIsCorrect ()
      {
          if(passwordInput == correctPassword )
          {
              passwordField.text = "Access granted";
              numberOneAdded = true;
              numberTwoAdded = true;
              numberThreeAdded = true;
              numberFourAdded = true;
              keypadActive = false;
              if(affectedDoor.lockedWithKeypad == true )
              {
                  affectedDoor.isDoorLocked = false;
              }
              StartCoroutine (WaitToLeaveAutomatic ());
          }
          else
          {
              passwordField.text = "Access denied";
              passwordInput = "";
              numberOneAdded = false;
              numberTwoAdded = false;
              numberThreeAdded = false;
              numberFourAdded = false;
          }
      }
      IEnumerator WaitToLeaveAutomatic ()
      {
          yield return new WaitForSeconds (2);
          LeaveKeypad ();
      }
  }
 

why is this so? thanks for help!