I guess we shall not agree.
Mike is in possession of property stolen from Brian's family 75 years ago. Mike has no idea it's stolen. Brian's family has two choices to get it back. Demand it and wait as long as it takes and pay whatever it costs to get through the legal challenges or each member of the family can pay 1 US cent and get the item back immediately.
Both choices are "within their rights", certainly.
As I said before, the cost of that rifle is 0.0016 US pennies per polish person.
Me? I'd pay it. You, you'd sue. It's all good. Neither of us has to understand the other.