What is the ruling on shunning and severing ties with the brother who raped my daughter and prevented my sons from visiting him?

Boycotting is legislated if it serves a legitimate Shariah purpose, such as deterring the boycotted person from sin. Otherwise, drawing near to them and offering advice is more appropriate. It is not permissible for a Muslim to boycott their brother for more than three days unless there is a legitimate Shariah excuse, such as an innovation (bid'ah) or open transgression (fisq). It may be recommendable to refrain from greeting people of innovation and open disobedience as a form of reprimand and deterrence. Boycotting varies depending on the boycotters, their strength, and their weakness. If boycotting him achieves a greater benefit, by weakening evil and making it hidden, then it is legislated. Otherwise, it is not; rather, reconciliation would be more beneficial. This is why the Prophet, peace and blessings be upon him, would reconcile with some people and boycott others. It is advisable to forgive and pardon the brother if he repents, while also protecting and safeguarding the children.