Instantiate problem with multiple objects from an array

hello friends , i am trying to do some targeting GUI using NGUI but ran into some problem , here is it:

1:- i have a topdown shooter , the player gets a targeting brackets for near enemy's when near 100 units.

2:- i did it right with the normal GUI from unity and here is the script:

 function OnGUI() {
     lastPosition = Camera.main.WorldToScreenPoint(hitColliders[0].gameObject.transform.position);
                 var dist = lastPosition - playerObject.transform.position;
                 var dim = hitColliders[i].gameObject.renderer.bounds.size;
                 
                 var midDimx = dim.x * 120;
                 var midDimy = dim.y * 120;
                 
                 var finalDim = Vector2(midDimx/2,midDimy/2);
                 
                 var distfinalxplus = Mathf.RoundToInt(dist.x) - Screen.width;
                 var distfinalyplus = Mathf.RoundToInt(dist.y) - Screen.height + 34;
                 distfinalx = Mathf.RoundToInt(dist.x);
                 distfinaly = Mathf.RoundToInt(dist.y) + 34;
                 
                 if(lastPosition.x >= Screen.width){
                     GUI.Label(Rect(Screen.width + adjstGUI.x - 70, -lastPosition.y + adjstGUI.y + Screen.height + 20, 80,80),"Dist " + distfinalxplus);
                     GUI.DrawTexture(Rect(Screen.width + adjstGUI.x - 10, -lastPosition.y + adjstGUI.y + Screen.height + 20, 30,30), aTextureright, ScaleMode.ScaleToFit, true);
                 }
                 if(lastPosition.x <= 0){
                     GUI.Label(Rect(0 + adjstGUI.x + 95, -lastPosition.y + adjstGUI.y + Screen.height + 20, 80,80),"Dist " + -distfinalx);
                     GUI.DrawTexture(Rect(0 + adjstGUI.x + 60, -lastPosition.y + adjstGUI.y  + Screen.height + 20, 30,30), aTextureleft, ScaleMode.ScaleToFit, true);
                 }
                 if(lastPosition.y <= 0){
                     GUI.Label(Rect(lastPosition.x + adjstGUI.x + 20, Screen.height + adjstGUI.y - 50, 80,80),"Dist " + -distfinaly);
                     GUI.DrawTexture(Rect(lastPosition.x + adjstGUI.x + 20, Screen.height + adjstGUI.y - 30, 30,30), aTextureDown, ScaleMode.ScaleToFit, true);
                 }
                 if(lastPosition.y >= Screen.height){
                     GUI.Label(Rect(lastPosition.x + adjstGUI.x + 20, 0 + adjstGUI.y + 95, 80,80),"Dist " + distfinalyplus);
                     GUI.DrawTexture(Rect(lastPosition.x + adjstGUI.x + 20, 0 + adjstGUI.y + 60, 30,30), aTextureup, ScaleMode.ScaleToFit, true);
                 }
                 GUI.DrawTexture(Rect(lastPosition.x - finalDim.x, -lastPosition.y - finalDim.y + Screen.height, 120 * dim.x,120 * dim.y),aTexture,ScaleMode.ScaleToFit,true);
             }
         }
     }
     
 }
 }

this code is working fine with the old GUI.

3:- now i want to upgrade to NGUI which is much better but as i understand i must spawn an Object , so i did this script:

 function Update () {
     hitColliders = Physics.OverlapSphere(transform.position, searchrange , mask.value);
     for (var i = 0; i < hitColliders.Length; i++) {
         if(hitColliders[i] != null){
             if(hitColliders[i].gameObject.tag == "Enemy"){
                 
                 numberOfEnemyDetacted = hitColliders.Length;
              
                 if(i >= hitColliders.Length){
                     targetPos = Camera.main.WorldToScreenPoint(hitColliders[i].gameObject.transform.position);
                     var markerSpawned = Instantiate(markerUITextureObject,Vector3(targetPos.x,targetPos.y,0.0),Quaternion.identity);
                     markerSpawned.transform.position = cameraGUI.ScreenToWorldPoint(Vector3(targetPos.x,targetPos.y,0.0));
                 }
                 targetValue = hitColliders.Length;
             }
         }
     }
 }

this code is the problem , wt i want is to spawn an object that have a texture on multiple objects , this problems i get is: a:-using the code above just spawns soo many marker objects that lags unity and hungs. B:-i want it to spawn marker objects on only the objects near 100 range , but also removes marker objects if any objects leaves the detection range and also adds marker objects to any object enters detection range c:-marker objects just gets spawned on the center and does not follow objects

note : some of the code above have some debugging code.

thanks to anyone who tries to help me

cheers