Clicking on one object to destroy a specific number of tagged objects dragged sidebyside

something like this is what you need to detect if objects are next to each other. As for destroying objects when something is clicked, add something like this to the object you want clicked

 GameObject[] objects;
 string yourTag;
 
 bool objectsNextToEachOther; //set this from another script
 
 void Awake()
 {
     objects = GameObject.FindGameObjectsWithTag(yourTag);
 }
 
 void OnMouseDown() //monobehaviour method that senses if an object is clicked
 {
     if (objectsNextToEachOther)
     {
         foreach (GameObject obj in objects)
         {
             Destroy(obj);
         }
     }
 
 }