Is it permissible for a father to expose himself to his son's wife from his (the father's) wife, and likewise to the wives of his brothers, knowing that he is 65 years old? And is it permissible for a mother to expose herself to the husbands of her husband's daughters or the husbands of her sisters?

It is not permissible for a father to look at his brother's wife merely because she is his brother's wife, nor to look at the wives of maternal uncles. Similarly, it is not permissible for a mother to uncover herself before the husbands of her step-daughters (from her husband's other wives) if she has not breastfed them. As for the husbands of sisters, they are mahram to the mother if these sisters are her sisters from her mother's side, or if she has breastfed them; based on the Almighty's saying: "and your wives' mothers." However, if they are her sisters from her father's side and she has not breastfed them, then it is not permissible for her to uncover herself before them.