Next of Kin Letter is a document used to confirm who is the closes relative of the deceased that are still living. If you are not the sole next of kin, you must also provide notarized renunciations from other relatives who qualify to administer the estate.To close a bank account on behalf of someone who has passed away, you must have legal authority to manage the account. Title 20 CHAPTER 31 DISPOSITIONS INDEPENDENT OF LETTERS; FAMILY EXEMPTION; PROBATE OF WILLS AND GRANT OF LETTERS Next-of-kin: Someone's closest living relative; may include a spouse, child or other close blood relative.