Can the green spots in these coins be copper chloride?
This phenomenon is relatively common among jewellers and silversmiths and they call it verdigris. This verdigris can be copper oxide, copper acetate, copper carbonate and even copper chloride. The former options are more likely, but copper chloride can actually be a possibility if you live close to the sea.

Perhaps relevant to your father: verdigris can be cleaned by applying a mildly acidic solution to it, such as lemon juice or vinegar. The formation of verdigris can be prevented by keeping the metal dry as this kind of corrosion is typically formed by contact of the metal with moisture.