It should be double counted since we need to do something about it. Cousin could pay the carbon tax on gas for usage, and owner could pay a carbon tax for milage usage at the end of the year.

I’m aware that this is a non-starter, but it would be a good start for getting overall emissions down. The billionaires should also pay a carbon tax above and beyond what the corporations pay, as a double incentive to stop polluting the planet for profit. Take away the profit, and companies will change.