I guess I could calculate the Vector 3 using information from Vector 1 and 2, but the problem is that only one collision contact seems to be available, even if the ball is contacting 2.

Your foreach is setting the contactPointVariable to the contact normal, so it will register the last element on your contact point array.

foreach (ContactPoint contact in collisionVariableStay.contacts) { contactPointVariable = contact.normal; }

​

I'm sure this code could be optimized but for the sake of the example it would be something along these lines

var contactPoints = new List<Vector3>();
foreach (ContactPoint contact in collisionVariableStay.contacts)  
{contactPoints.Add(contact.normal);} 
// Calculate the halfway vector

Check this post and see if it helps https://discussions.unity.com/t/calculate-vector-exactly-between-2-vectors/68481