Fuel for Thought

[Jonas]

Have the wife (and her mother) return as far as they can get. You go and meet them at that point in the other vehicle and bring them home. You may even be able to tow the car that is out of gas, but if not, you still have everyone home and safe.

You might also want to take some tubing to siphon gasoline from one vehicle to another if that would allow you to get both vehicles home.

Finally, had you been aware of the situation, you might have gotten your mother-in-law back to your home before things truly devolved into mayhem.