A surreal story! Kidnapping, ransom demands for milk and cookies, banks with "no service" during an emergency, then a last-minute change of heart from the kidnappers? Sounds like a bad movie plot. But hey, if it did happen, congrats on getting your brother back!
Kidnappers stay in the forest, and they usually ask for food items plus ransom. Some of them can't buy in the market. I told you that they were angry and broke my brother's legs.
But there's a plot hole in your story. Bitcoin wouldn't have magically solved your "outrageous ransom" problem either. If you couldn't afford the fiat, what makes you think you'd suddenly have a pile of Bitcoin lying around that was enough? Centralized or not, if you don't have the funds, you don't have the funds.
Simple answer to your question. If I had a Bitcoin backup, I would have simply sold it in an exchange and sent the money to the money changers. And I would have immediately received cash that would be used for payments.