Balanced forces do not change the motion of an object

correct, unbalanced or unequal forces do change the motion of an object.

I. E one person is pushing the ball to the right at 12 newtons, and another person on the other side is pushing the ball to the left at 12 newtons.

The ball simply does not move because neither is exerting more force than the other. They are equal.

However if the person pushing the ball to the right was using the force of 14 newtons then the ball would move to the right, regardless of the person on the otherside.

Have a blessed day!