What is the legal ruling regarding children being asked to repay their father's debt after he went bankrupt and sold his property, and what is the ruling regarding the father being asked to repay the value of the mortgage placed by the father of my sister's husband, knowing that the latter had previously prevented him from selling the project?

If a person guarantees the debt of the questioner's father, and then the guarantor's property is sold to repay the debt, the guarantor has the right to reclaim the price of the house from the one whose debt was guaranteed. If the debt concerns them as partners, then he may reclaim from his partner what exceeds his share. However, it is not permissible to demand that the debtor's children repay their living father's debt. These matters are decided by the Sharia judiciary.