How i can spawn enemies of different types???

I want to spawn 3 or 4 different type of enemies at same location? i have written a script which only spawns two type of enemies at same location i am new to unity and c# please helo me here is my spawn script... public GameObject enemy; public GameObject enemy1; public GameObject boss; public float speed = 5f; public bool ismoveright = true; public float min = -4f; public float max = 4f; public float padding = 3.5f; public float spawndelay = 3f;

 // Start is called before the first frame update
 void Start()
 {

    
         SpawnUntill();
        
   
 }

 //for adjusting enmies speed/movement
 void Update()
 {


     if (ismoveright == true)
     {
         transform.position += Vector3.right * speed * Time.deltaTime;
     }
     if (transform.position.x >= max)
     {
         ismoveright = false;

     }
     if (transform.position.x <= min)
     {
         ismoveright = true;

     }
     if (ismoveright == false)
     {
         transform.position += Vector3.left * speed * Time.deltaTime;
     }
     ScreenSizer();

     if (CheckDestroyedEnemy())
     {  
         SpawnUntill1();
         if (CheckDestroyedEnemy())
         {
             SpawnUntill2();
         }


     }
 }
 //for generating enemies one by one not together

 void SpawnUntill()
 {
     Transform position = ChildPosition();
     if (position)
     {
         GameObject Enemyprefab = Instantiate(enemy, position.transform.position, Quaternion.identity) as GameObject;
         Enemyprefab.transform.parent = position;
     }

     if (ChildPosition())
     {
         Invoke("SpawnUntill", spawndelay);
     }


 }
 void SpawnUntill1()
 {
     Transform position = ChildPosition();
     if (position)
     {
         GameObject Enemyprefab = Instantiate(enemy1, position.transform.position, Quaternion.identity) as GameObject;
         Enemyprefab.transform.parent = position;
     }

     if (ChildPosition())
     {
         Invoke("SpawnUntill1", spawndelay);
     }


 }
 void SpawnUntill2()
 {
     Transform position = ChildPosition();
     if (position)
     {
         GameObject Enemyprefab = Instantiate(boss, position.transform.position, Quaternion.identity) as GameObject;
         Enemyprefab.transform.parent = position;
     }

     if (ChildPosition())
     {
         Invoke("SpawnUntill2", spawndelay);
     }


 }
 
 //for moving enemies accordng to secreen size
 public void ScreenSizer()
 {

     float distancetoscreen = transform.position.z - Camera.main.transform.position.z;
     Vector3 leftmost = Camera.main.ViewportToWorldPoint(new Vector3(0, 0, distancetoscreen));
     Vector3 rightmost = Camera.main.ViewportToWorldPoint(new Vector3(1, 0, distancetoscreen));
     min = leftmost.x + padding;
     max = rightmost.x - padding;
 }
 //for checking all enemies are destroyed or not so we can produce new enemies
 bool CheckDestroyedEnemy()
 {
     foreach (Transform childobj in transform)
     {
         if (childobj.childCount > 0)
         {
             return false;

         }
     }
     return true;
 }
  
 //for generating enemies on positon in which it appers first time 
 Transform ChildPosition()
 {

     foreach (Transform childobj in transform)
     {
         if (childobj.childCount == 0)
         {
             return childobj;

         }
     }
     return null;
 }