How to spawn random objects with differents vector 3?

Think your problem here is probably in the if / else statements. Random.Range() returns a float between the two numbers you set (https://docs.unity3d.com/ScriptReference/Random.Range.html) so only the default on your if / else statements will be true. What you could do is Mathf.RoundToInt() your randoms (https://docs.unity3d.com/ScriptReference/Mathf.RoundToInt.html) so that they're integers. Could look something like this:

 int randomObject;
  void Start()
  {
      InvokeRepeating("Spawner", 4f, 1f);
      StartCoroutine(Spawner());
  }
  IEnumerator Spawner()
  {
      yield return new WaitForSeconds(1);
      Vector3 temp = SpikeHolder.transform.position;
      temp.y = Random.Range(-2.5f, 2.5f);
      Vector3 temp2 = Missile.transform.position;
      temp2.y = Random.Range(-3.5f, 3.5f);
      Vector3 temp3 = MovingSpikeUp.transform.position;
      Vector3 temp4 = MovingSpikeDown.transform.position;

      // THIS PART!! 
      randomObject = Mathf.RoundToInt(Random.Range(1, 4));
 
      if(randomObject==1)
      {
          Instantiate(SpikeHolder, temp, Quaternion.identity);
          InvokeRepeating("Spawner", 4f, 1f);
          StartCoroutine(Spawner());
      }
      else if(randomObject==2)
      {
          Instantiate(Missile, temp2, Quaternion.identity);
          InvokeRepeating("Spawner", 4f, 1f);
          StartCoroutine(Spawner());
      }
      else if(randomObject==3)
      {
          Instantiate(MovingSpikeUp, temp3, Quaternion.identity);
          InvokeRepeating("Spawner", 4f, 1f);
          StartCoroutine(Spawner());
      }
      else
      {
          Instantiate(MovingSpikeDown, temp4, Quaternion.identity);
          InvokeRepeating("Spawner", 4f, 1f);
          StartCoroutine(Spawner());
      }

Although I didn't try that code out myself, that's the idea of what you wanna do. Not totally sure what you want to happen with the temp vectors, if you want them to be whole numbers you could do the same thing on each axis.

You're calling InvokeRepeating multiple times, starting the coroutine multiple times, quite unpredictable :)

Just calling InvokeRepeating solves your problem of spawning every X seconds.

You don't specify exactly what your problem is. Are you having an exception? Nothing happens? Is the first object instantiated but then it stops?

The following code should work if all your variables are assigned. You can make it more elegant by using a switch statement, and using arrays for holding the prefabs and their default positions.

 int randomObject;
  void Start()
  {
      InvokeRepeating("Spawner", 4f, 1f);
  }
  void Spawner()
  {
      Vector3 temp = SpikeHolder.transform.position;
      temp.y = Random.Range(-2.5f, 2.5f);
      Vector3 temp2 = Missile.transform.position;
      temp2.y = Random.Range(-3.5f, 3.5f);
      Vector3 temp3 = MovingSpikeUp.transform.position;
      Vector3 temp4 = MovingSpikeDown.transform.position;
      
      randomObject = Random.Range(1, 4);
      if(randomObject==1)
      {
          Instantiate(SpikeHolder, temp, Quaternion.identity);
      }
      else if(randomObject==2)
      {
          Instantiate(Missile, temp2, Quaternion.identity);
      }
      else if(randomObject==3)
      {
          Instantiate(MovingSpikeUp, temp3, Quaternion.identity);
      }
      else
      {
          Instantiate(MovingSpikeDown, temp4, Quaternion.identity);
      }