Answers:
Once the owner of the account died the authorized user status
terminated. Here the point to be noted that the authorized user in not a co-owner
of the account. As you have says that there is no assets on his name then just inform
them that there is no property as such in the name of your brother.
May be possible that debt was probably re-sold and now the
collection agency is trying to get anything out of it.
Note: This is not a
legal advice only for general information, and this answers does not have any relationship with Collection Agency and client.