Is it permissible for me to shake hands with my mother-in-law? Is it permissible for me to shake hands with the wives of my father's uncles
taking into consideration that they are old? Is it permissible for me to shake hands with an old woman? Is it permissible to greet women by heads instead of hands? Some people say that it is permissible to lower your head to a woman to place her hand on it to greet you, especially when she is old.
it is permissible for a man to shake hands with his mother-in-law and greet her because he is one of her Mahrams (unmarriageable relatives).
it is not permissible for a man to shake hands with the wives of his uncles or the uncles of his father even if they are old because he is not one of their Mahrams.
it is permissible for a person to kiss the head of old men, scholars and religious men out of respect. Likewise, he may kiss the head of his female Mahrams (spouse or unmarriageable relative). (Part No. 17; Page No. 363) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.