A: If they were legally divorced, the lawyer should have no need for a death certificate unless the lawyer is trying to claim an asset. I would not give it to the lawyer and get an explanation of why it is needed.
A: I agree with my partner that you need to register a registered gun that is bequeathed to you. However, there are situations where your bequest is unregistered and this requires knowing what types of guns they are and whether you need to involve the police/ law enforcement. You must discuss this with a lawyer. Are you the executor? I suggest you work through a lawyer.