Story sounds fishy, but would someone plant them there to create a “mystery” if they were really valuable coins?
I would think they would be rather valuable.
Age doesn’t make a coin valuable, rarity and interest does. For example, there are literally millions of old Roman era coins out there that you can get for pocket change.
Haven’t researched these coins, I’m sure they’re worth something decent, but probably even more to collectors if they are determined to be actually historic and not recently deposited where they were found.
One of them has been identified as a 16 maravedi. These are on sale through eBay at around $5.