What can we do so that my father, who is over 85 years old, may pray, given that he cannot maintain physical or clothing purity due to his inability to control defecation or urination, and is an expiation (kaffarah) obligatory upon him for not praying?

If the father has lost his mind, then he is no longer subject to religious obligations such as prayer, and there is no expiation due from him, for the Prophet, peace and blessings be upon him, said: "The pen has been lifted from three: from the child until he reaches puberty, from the sleeper until he awakens, and from the insane person until he regains his sanity." However, if he is of sound mind but cannot control his purity, he is treated like a person with incontinence; he should be assisted in performing ablution for each prayer after its time has begun, and what has afflicted his clothes from impurity is excused.