These coins were never put into circulation. That means they are stolen property.
They weren't the legal property of the family.
Confiscate means to sieze private property for the government. These coins were never private property.
Supposedly... but the burden of proof is on the Government here. They've already admitted that they can't prove it.
That should be the end of the story. Assuming we all still want to pretend that we live in a country ruled by Law.