Using multiple instances of the same script

I am making a game with multiple audio tracks that a player can turn on and off via hitting or missing certain colliders. There are 4 layers of audio tracks that I have working well but there is a script that needs to be applied to all layers yet only affect the sounds of the particular track it resides on.

What I have is a parent object called Layer1, Layer2, etc. that have an Audio Source on it. These have a child object of a collider that will set the audio playing if hit. At the moment every time I hit an object with this script, it starts the track again. I want it that if another object has been hit and set the track playing, then if this one gets hit it will ignore it. This script is as follows:

 public class PlayNote : MonoBehaviour {
     
     public GameObject sound;
 
     void Start () 
     {
         sound = GameObject.Find(this.transform.parent.name.ToString());
         sound.GetComponent("AudioSource");
     }
     
     void OnTriggerEnter(Collider other) 
     {
         if(!AlreadyPlaying.isPlaying)
         {
             AlreadyPlaying.isPlaying = true;
             sound.audio.Play();
             this.gameObject.SetActive(false);
         }
         if(AlreadyPlaying.isPlaying)
         {
             this.gameObject.SetActive(false);
         }
     }
 }

I have a child of this that also has a collider that when hit will stop the audio playing:

 public class StopPlaying : MonoBehaviour {
 
 public GameObject sound;
 
 void Start()
 {
     sound = GameObject.Find(this.transform.parent.transform.parent.name.ToString());    
     sound.GetComponent("AudioSource");
 }
 void OnTriggerEnter(Collider other)
 {
     AlreadyPlaying.isPlaying = false;
     sound.audio.Stop();
 }
 }

The last script is the one that I can't get to work with it all and this is the one that tells the other scripts weather or not the track is already playing and sits on the Layer1/Layer2 game objects that contain the sound:

 public class AlreadyPlaying : MonoBehaviour {
 
 public bool isPlaying;

 void Start () 
 {
 isPlaying = false;
 }
 }

When it runs, the AlreadyPlaying script affects all instances of the bool, not the one specific to the gameobject that the script is sitting on. I have tried using GetComponent("AlreadyPlaying") but I cant seem to access the boolean on each specific layer.

Any help much appreciated.