§ 1. The following are qualified to challenge a marriage: 1° the spouses; 2° the promoter of justice when nullity has already become public, if the convalidation of the marriage is not possible or expedient. § 2. A marriage which was not accused while both spouses were living cannot be accused after the death of either one or both of the spouses unless the question of validity is prejudicial to the resolution of another controversy either in the canonical forum or in the civil forum. § 3. If a spouse dies while the case is pending, however, can. 1518 is to be observed.
Source: Code of Canon Law (Vatican.va)