What is the ruling on supplicating against a tyrannical daughter-in-law, and what is the ruling on fasting three days as expiation for this supplication? Is it permissible not to eat her food? And is it permissible to purchase a house through an interest-based loan in Western countries to دفع ظلم الأبناء (ward off the oppression of the children/prevent injustice from the children)?

The son's wife should respect and honor her husband's mother. The son should encourage his wife to do so. The husband's mother should help her son's wife in her dutifulness towards her by treating her kindly. As for supplicating against the oppressor, it is permissible, according to the Almighty's saying: "{Allah does not like the public utterance of evil speech, except by one who has been wronged}" [Quran 4:148]. Buying a house with an interest-based loan is not permissible. Whoever does so must offer sincere repentance, and is not obligated to sell the house if he is in need of it. The saying "fate willed it" is not permissible.