Is it wrong to keep the relationship superficial with a brother who seized a portion of the inheritance and refused to return it, knowing that the mother is pressuring for forgiveness?

If a brother disposes of his sister's property without her consent, he has committed a reprehensible act, due to the words of Allah Almighty: ﴿O you who have believed, do not consume one another’s properties wrongfully﴾, and due to the words of the Prophet, peace and blessings be upon him: "The property of a Muslim person is not lawful to take except with his willing consent." The mother does not have the right to compel her daughter to forgive her brother or to waive the money, and the daughter has the right to demand it from him.

Forgiving the brother, out of filial piety towards the mother and maintaining ties of kinship, may be compensated by Allah with something better, based on the words of the Prophet, peace and blessings be upon him: "Indeed, you will not abandon anything for the sake of Allah – Glorified and Exalted is He – except that Allah will give you something better than it." As for how to deal with him, it depends on what is customarily considered maintaining ties or severing them. It is preferable to deal with him normally to please the mother, for the pleasure of the Lord is in the pleasure of the parent.