15 CFR §80.3

1. (a)Census information relating to a deceased person may be released only to a parent, child, grandchild, brother, sister, spouse, insurance beneficiary, or the executor or administrator of a deceased person's estate. The request must be signed by a person entitled to receive the information as provided herein, state the relationship of the applicant to the deceased, and include a certified copy of the death certificate or other adequate proof of death. The request of an executor or administrator must be accompanied by a certified copy of the court order of appointment.
2. (b)Except for a spouse, a person related to the deceased person through marriage, such as an in-law relationship, is not eligible to request Census information on the deceased, whether or not the applicant was a member of the household of the deceased.