Is the husband sinful if he divorces his wife while she is unwilling to be divorced, knowing that the husband's mother was instigating her son to divorce his wife? And is the wife sinful if she supplicates against her husband and his mother?

Allah decreed the failure of this experience, and perhaps there is good in that. The sister should forget this young man and her failed experience, and not occupy herself with supplicating against him or feeling wronged. Rather, she should turn to Allah in prayer to grant her a righteous husband and to enrich her from His bounty, in fulfillment of His saying: "But if they separate [by divorce], Allah will enrich each of them from His abundance. And Allah is ever encompassing and wise." A man divorcing his wife out of necessity is neither forbidden nor an injustice, so it is not permissible for her to supplicate against him merely because he divorced her.