GameObject list doesn't decrease.

Hi I have this code for the enemies:

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public class EnemyEngine : MonoBehaviour {
     //*********Member Variables**********//
     public float enemyHealth = 100.0f;
 
     //*****List****//
     public List<GameObject> allEnemies;
     public Transform selectedEnemy;    
     private Transform enemyTransform;
     private bool enemyIsAlive;
 
     void Start () {
         enemyIsAlive = true;
         allEnemies = new List<GameObject>();
         selectedEnemy = null;
         enemyTransform = transform;
         AddEnemies();
     }
 
     //What these next two functions do is adds all the enemies in the scene into a list.
     void AddEnemies()
     {
         GameObject[] zombieEnemy = GameObject.FindGameObjectsWithTag("zombie");
         GameObject[] mummyEnemy = GameObject.FindGameObjectsWithTag("mummy");
         foreach(GameObject enemy in zombieEnemy)
         {
             AddInList(enemy.gameObject);
         }
         foreach(GameObject mummy in mummyEnemy)
         {
             AddInList(mummy.gameObject);
         }
     }
 
     void AddInList(GameObject enemy)
     {
         allEnemies.Add (enemy);
     }
 
     void RemoveNull()
     {
         foreach(GameObject nullOBJ in allEnemies)
         {
             if(nullOBJ.gameObject == null)
             {
                 allEnemies.Remove(nullOBJ.gameObject);
             }
         }
     }
     bool IsEnemyDead()
     {
         return enemyIsAlive;
     }
 
     // Update is called once per frame
     void Update () 
     {
 
         if(IsEnemyDead())
         {
             if(enemyHealth <= 0)
             {
                 enemyIsAlive = false;
             }
             else
             {
 
             }
         }
         else
         {
             allEnemies.Remove(this.gameObject);
             Debug.Log (allEnemies.Count);
             Destroy(this.gameObject);
         }
     }
 }

Any idea of how to do this properly. Thanks.

Edit: The script is placed individually on each enemy. What i have seen is that if i don't destroy the object and i just remove the item from the list then it updates and removes it, however on the other enemies it is still on the list.

EDIT: I managed to do it. What i needed to do was check the gameobjects from zombieenemy and mummyenemy, and then if it is null then remove it from the point in allEnemies

:)