OY, that is a VERY bad situation. I am so sorry for the obvious agita this will bring you in rectifying the situation. Can you confront the family member, let him/her know that you knwo and what steps you plan to take to resolve the problem? If it is a younger person, some tough love may be needed. This is a crime, and the person should not get off the hook for it, IMO, because tyhe next person whose identity they steal will slap them in jail when they catch them. As a relative, you may have other means at your disposal to deal with this.