Issue With Simultaneous ReadPixels Calls

Hi, first time asking, really couldn't find the answer I was looking for.

I have these entities called "torches" that receive a portion of the a camera's view port via ReadPixles, and uses it as it's texture.

It works, but I get into problems when I have multiple torches calling for a Screen Grab in the same frame. I have tried using co-routines, but when I do, I don't get a texture. I am probably doing it wrong.

If multiple calls are done in the same frame, the first call receives the texture, while the others get the default purple one.

How can I edit my code to make it readpixels multiple times in the same frame without having to attach a camera to each torch?

Attach is picture (I hope)

Thanks,

Ed

Code in Screen Grabber

 using UnityEngine;
 using System.Collections;
 
 public class ScreenGrabber : MonoBehaviour {
     private bool grab;
     private Renderer display;
     private Texture2D tex;
     private int pixelDiam;
     private int pixelX;
     private int pixelY;
 
     //Takes a picture of where it is, and then applies it to the object
     //due to screen dimensions and game dimensions being different, it has to calcualte what resolution it needs to be
 
     void OnPostRender() {
         if (grab) {
             tex = new Texture2D(pixelDiam, pixelDiam);
             tex.ReadPixels(new Rect(pixelX,pixelY,pixelDiam,pixelDiam),0,0);
             tex.Apply();
             display.material.mainTexture = tex;
             grab = false;
         }
     }
     
     public void setGrab(Renderer rend, int size, Transform target)
     {    
         //Finding the co ords on screen that are 0,0 for the texture;
         pixelX = (int)camera.WorldToScreenPoint (target.position + new Vector3 (size, 0, 0)).x;
         pixelY = (int)camera.WorldToScreenPoint (target.position - new Vector3 (0, size, 0)).y;
         //Finding the diametre in pixels of the cirlce, by getting the sccreen pos of either side of the cirlces centre
         pixelDiam = ((int)camera.WorldToScreenPoint(target.position - new Vector3 (size,0,0)).x - pixelX);
         display = rend;
         grab = true;
     }
 }

Code that calls it

         //getting the texture that will be applyed to it
         GameObject camera = GameObject.FindGameObjectWithTag ("MainCamera");
         camera.GetComponent<ScreenGrabber>().setGrab(renderer, (int)maxSize, transform);