>> They’re going to donate most of the proceeds to charity. <<
Both from a philanthropic viewpoint and from a tax viewpoint, they’d do better to donate the coins directly to various tax-exempt charities, rather than sell the coins and then donate the proceeds.
The couple also wisely claims they found the coins on their own property.
It doesn’t say they are donating most of the money. It says the plan is to sell the coins and pay off bills and donate to some charities.