Is it permissible for a daughter to clean her sick father who is suffering from severe diarrhea and to uncover his awrah, given that he has a son who could do it?

Removing impurities from an incapacitated father is an act of piety. It is forbidden by Islamic law to look at or touch the private parts of another, whether he is a father or anyone else, based on Allah's saying: "Tell the believing men to reduce [some] of their vision and guard their private parts," and the Prophet's (PBUH) saying: "Avert your gaze." The wife should handle this; otherwise, the son or other men have priority over the daughter. If no men are available, then it is permissible for the daughter to do so out of necessity. Therefore, there is no sin upon you both for what you have done, due to the absence of anyone else.