The World Federation One Stop Fiqh

Ruling 2732

If a person appoints two individuals as his executors and one of them dies, or becomes insane or a disbeliever (kāfir), then, if it can be understood from the wording of the will that in such a situation the other person is to act as executor on his own, the will must be executed in this way; otherwise, a fully qualified jurist will appoint another person in his place. If both of them die or become insane or apostate, the fully qualified jurist will appoint two people. However, if one person is able to execute the will, it will not be necessary for him to appoint two people.