Collision Events - Executing Code once per Collision Across Multiple Objects

I'm trying to create a script to handle collision between two objects, which are balls.

For example, a billiards game, but instead of the cue ball coming to a complete stop when it hits another ball. I want the cue ball to reverse directions, as well as applying its impulse to the ball it hit. Here is my code:

  private void OnTriggerEnter2D(Collider2D collision)
     {
 
         if (gameObject.tag == "Ball")
         {
             if (collision.gameObject.tag == "Ball")
                // Check if the ball we are executing on is a moving ball
                 if (System.Math.Abs(Velocity) > 0) 
                 {
                     Velocity = -Velocity;
                 }
                 // If this ball wasn't already moving
                 else 
                 {
                         Velocity = collision.gameObject.GetComponent<Ball>().Velocity;      
                 }
        }
 }

The issue I'm having is that, when a moving ball contacts a non-moving ball, depending on the order the collision event executes, it can do one of two things:

• Execute order correctly, ie. Non-Moving ball starts moving in the correct direction and moving ball switches directions

• Order is incorrect ie. Moving ball switches directions, but when non-moving ball sets it's new, non-zero, velocity, it sets it to the 'switched' direction on the original moving ball. So, now both balls are moving in the same direction.

What changes do I need to make sure the collision event effects both balls, independently, but correctly?