Is it permissible for us to fast the days that our sick father, who is incapable of fasting and feeding the poor, missed?

If a person is unable to fast, an inability that is not expected to cease, then he may break his fast and must pay a fidyah (expiatory feeding); based on the Almighty's saying: "And upon those who are able to fast, but with difficulty, is a ransom of feeding a poor person," and what Ibn Abbas said in its interpretation. If he cannot find the fidyah, it remains a debt upon him until he is able to pay it. Substitution in fasting for him while he is alive is not permissible. However, if he has lost his sanity, then neither fasting nor expiation is obligatory for him, as accountability is lifted from him; based on the Prophet's (peace and blessings be upon him) saying: "The pen has been lifted from three."