Is a woman sinful if she is forced to shake hands with her male cousin (her mother's brother's son), her male maternal aunt's son, or her male paternal uncle's son, after she has learned of the impermissibility of that?

Shaking hands with non-mahram (definition) men is forbidden for a woman, and the prayer (du'a) of relatives who curse her for refusing to shake hands will not be answered, because it is oppression and aggression. If she is forced to shake hands under severe threat, there is no sin upon her. However, threatening to break off an engagement is not considered a valid form of duress. She must repent to Allah and clarify the ruling of Islamic law to her relatives.