There are tests of truth: Conformity to reality, observable, corroboratable, logical, consistency. That's how we settle the dispute.

In the Bible, I'm not aware of Satan ever saying anything that was true. It doesn't conform to any of the tests for truth. God, by contrast, is full of truth. The dispute is a non-contest. Governing a kingdom is not a criteria for determination of truth. Some of the worst men and women of history have been political leaders.

How does humans being in this circle of “life” settle a dispute about which one of God and Satan is right?

Especially since they both have their own spiritual kingdom and way of governing