Camera to centre on player, but never exceed "map" bounds

I am creating a game which has up to 4 orthographic cameras (for up to 4 players), which take up various amounts of the screen, depending on the amount of players.

I have a script which controls all the cameras, setting their position relative to the players they are watching.

What I want to achieve is a simple overhead-runner style of movement, whereby the camera will follow the player, but not go outside the bounds of the map.

I have the code to move the cameras, within a specific bounds, already in place. The question is, how do I FIND the minimum and maximum values? I have a Map object, placed at 0,0 - so I guess I need need to somehow find the top and bottom corners of that object, in relation to the cameras. How can I do this?

My current code is below:

 if((trackPlayer1 == null))
 {
     camPlayer1.transform.position = this.transform.position;
 }
 else
 {
     camPlayer1.transform.position = new Vector3(Mathf.Clamp(trackPlayer1.transform.position.x, minX, maxX), Mathf.Clamp(trackPlayer1.transform.position.y, minY, maxY), camPlayer1.transform.position.z);
 }
 if((trackPlayer2 == null))
 {
     camPlayer2.transform.position = this.transform.position;
 }
 else
 {
     camPlayer2.transform.position = new Vector3(Mathf.Clamp(trackPlayer2.transform.position.x, minX, maxX), Mathf.Clamp(trackPlayer2.transform.position.y, minY, maxY), camPlayer2.transform.position.z);
 }
 
 if((trackPlayer3 == null))
 {
     camPlayer3.transform.position = this.transform.position;
 }
 else
 {
     camPlayer3.transform.position = new Vector3(Mathf.Clamp(trackPlayer3.transform.position.x, minX, maxX), Mathf.Clamp(trackPlayer3.transform.position.y, minY, maxY), camPlayer3.transform.position.z);            
 }
 
 if((trackPlayer4 == null))
 {
     camPlayer4.transform.position = this.transform.position;
 }
 else
 {
     camPlayer4.transform.position = new Vector3(Mathf.Clamp(trackPlayer4.transform.position.x, minX, maxX), Mathf.Clamp(trackPlayer4.transform.position.y, minY, maxY), camPlayer4.transform.position.z);
 }

UPDATE

Ok so using the code in this question(link), I have managed to get the boundaries working in the top-left camera, when the cameras are 'square' (as in the 4-player layout). However, the other cameras don't track properly at all, and in the rectangular 2-player mode, the top camera still goes too far left-and right. I'm pretty sure I know exactly which line of code is causing the problem... but I don't know what I need to do to fix it...

 SpriteRenderer spriteBounds = GameObject.Find("Map").GetComponentInChildren<SpriteRenderer>();
 
 if((trackPlayer1 == null))
 {
     camPlayer1.transform.position = this.transform.position;
 }
 else
 {
     float vertExtent = camPlayer1.orthographicSize;
     float horzExtent = vertExtent * Screen.width / Screen.height; //I guess the problem is here... but how do I fix this
 
     float leftBound = (float)(horzExtent - spriteBounds.sprite.bounds.size.x / 2.0f);
     float rightBound = (float)(spriteBounds.sprite.bounds.size.x / 2.0f - horzExtent);
     float bottomBound = (float)(vertExtent - spriteBounds.sprite.bounds.size.y / 2.0f);
     float topBound = (float)(spriteBounds.sprite.bounds.size.y / 2.0f - vertExtent);
 
     camPlayer1.transform.position = new Vector3(Mathf.Clamp(trackPlayer1.transform.position.x, leftBound, rightBound), Mathf.Clamp(trackPlayer1.transform.position.y, bottomBound, topBound), camPlayer1.transform.position.z);
 }
 if((trackPlayer2 == null))
 {
     camPlayer2.transform.position = this.transform.position;
 }
 else
 {
     float vertExtent = camPlayer2.orthographicSize;
     float horzExtent = vertExtent * Screen.width / Screen.height; //I guess the problem is here... but how do I fix this
 
     float leftBound = (float)(horzExtent - spriteBounds.sprite.bounds.size.x / 2.0f);
     float rightBound = (float)(spriteBounds.sprite.bounds.size.x / 2.0f - horzExtent);
     float bottomBound = (float)(vertExtent - spriteBounds.sprite.bounds.size.y / 2.0f);
     float topBound = (float)(spriteBounds.sprite.bounds.size.y / 2.0f - vertExtent);
 
     camPlayer2.transform.position = new Vector3(Mathf.Clamp(trackPlayer2.transform.position.x, leftBound, rightBound), Mathf.Clamp(trackPlayer2.transform.position.y, topBound, bottomBound), camPlayer2.transform.position.z);
 }
 
 if((trackPlayer3 == null))
 {
     camPlayer3.transform.position = this.transform.position;
 }
 else
 {
     float vertExtent = camPlayer3.orthographicSize;
     float horzExtent = vertExtent * Screen.width / Screen.height; //I guess the problem is here... but how do I fix this
 
     float leftBound = (float)(horzExtent - spriteBounds.sprite.bounds.size.x / 2.0f);
     float rightBound = (float)(spriteBounds.sprite.bounds.size.x / 2.0f - horzExtent);
     float bottomBound = (float)(vertExtent - spriteBounds.sprite.bounds.size.y / 2.0f);
     float topBound = (float)(spriteBounds.sprite.bounds.size.y / 2.0f - vertExtent);
 
     camPlayer3.transform.position = new Vector3(Mathf.Clamp(trackPlayer3.transform.position.x, leftBound, rightBound), Mathf.Clamp(trackPlayer3.transform.position.y, topBound, bottomBound), camPlayer3.transform.position.z);            
 }
 
 if((trackPlayer4 == null))
 {
     camPlayer4.transform.position = this.transform.position;
 }
 else
 {
     float vertExtent = camPlayer4.orthographicSize;
     float horzExtent = vertExtent * Screen.width / Screen.height; //I guess the problem is here... but how do I fix this
 
     float leftBound = (float)(horzExtent - spriteBounds.sprite.bounds.size.x / 2.0f);
     float rightBound = (float)(spriteBounds.sprite.bounds.size.x / 2.0f - horzExtent);
     float bottomBound = (float)(vertExtent - spriteBounds.sprite.bounds.size.y / 2.0f);
     float topBound = (float)(spriteBounds.sprite.bounds.size.y / 2.0f - vertExtent);
 
     camPlayer4.transform.position = new Vector3(Mathf.Clamp(trackPlayer4.transform.position.x, leftBound, rightBound), Mathf.Clamp(trackPlayer4.transform.position.y, topBound, bottomBound), camPlayer4.transform.position.z);
 }

Further Edit... I have now managed to get the first camera to track even when it's not a square size with the following code. It still doesn't work for any of the other cameras though

 if((trackPlayer1 == null))
         {
             camPlayer1.transform.position = this.transform.position;
         }
         else
         {
             float vertExtent = camPlayer1.orthographicSize;
             float horzExtent = vertExtent * (Screen.width * (camPlayer1.rect.width * 2)) / Screen.height; //I guess the problem is here... but how do I fix this??