How valid is the maternal uncle's Hajj, and is redoing it necessary, given that he is blind and performed some rituals with the help of his companions while omitting others? What is the ruling on his sister caring for him, attending to his hygiene and changing his clothes, with the possibility of his 'awrah being exposed due to his inability to control his actions?

If the maternal uncle is unable to complete the rituals of Hajj, such as Sa'y (walking between Safa and Marwa) and Tawaf (circumambulation of the Kaaba), due to an unresolvable impediment, and his companions perform these rituals on his behalf in the required manner, then that is sufficient. However, if the inability is not complete, then the Hajj is not considered complete because Sa'y and Tawaf al-Ifadah are essential pillars. If the maternal uncle is now completely incapacitated or has passed away and possesses wealth, then his family must perform Hajj on his behalf from his wealth.

Regarding the sister's care for her sick maternal uncle, her action is great and she will be rewarded for it. If the care requires direct contact with his 'awrah (private parts), then the default is for his wife to do so, if he has one, otherwise a man. If there is no one willing to do so, then it is permissible for the sister to attend to him, with caution to avoid touching or seeing the 'awrah except in cases of extreme necessity.