Is the questioner considered sinful if she saw parts of her brother's and mother's 'awrah while they were wearing short clothes above the knee, after she advised them to no avail?

It is permissible for a woman to wear tight, transparent, and short clothing only in front of her husband and her young, non-discerning children. It is not permissible to expose the thigh or part of it in front of women or mahrams. What is permissible to expose are the areas for ablution (wudu’) and adornment. Similarly, it is not permissible for a man to show any part of his thighs to anyone except his wife. Therefore, short shorts that expose the thigh are not permissible for either men or women to wear in front of each other, even if they are mahrams. You should advise your parents and siblings gently and patiently. If they do not respond, then strive to avert your gaze from the 'awrah (private parts).