Is borrowing with interest considered a necessity for recovering the father's inheritance from a brother who is withholding rightful shares, especially given factors that increase the urgent need, such as the situation of a divorced sister and the fear of the brother forging documents?

Dealing with Riba (usury/interest) is strictly forbidden. One must seek a permissible alternative to obtain money, such as Tawarruq (monetization), joining an employee savings group, or selling or mortgaging some property. If no permissible method is found, Riba is permissible out of necessity. This necessity is defined as reaching a point where one cannot find food, clothing, or rent for shelter, similar to someone forced to eat carrion. If there is no such necessity, then borrowing with Riba is not permissible.