Is an elder brother justified in shunning his sister for her refusal to marry a man who repented and embraced Islam after having caused her apostasy from Islam in the past?

All praise is due to Allah. The blessing of guidance is immense, and Allah must be thanked for it. One rejoices at the guidance of disbelievers and the return of Muslims to their faith, and we ask Allah to keep them steadfast. The parents are the first to rejoice at the guidance of their daughter and her return to Islam. The brother should not be a cause of harm to his family or a division within it, as he might cause his sister to fall into tribulation again. If the father approves of his daughter's marriage to this guided man, the brother has no right to object or threaten boycott; he may only express his opinion. It is not the brother's right to boycott his sister for marrying this man, as their marriage is not forbidden. While the marriage is permissible, we advise the father and the sister to reconsider their approval, to listen to dissenting opinions, to discuss the matter with sensible people, and to ascertain the sincerity of the suitor's Islam and his true desire for it. We ask Allah for guidance and righteousness for all.