What is the ruling of Islamic law on a brother who refuses his sister's marriage to a righteous man who proposed to her, and threatens suicide or emigration if the marriage takes place, thereby hindering his sister's marriage and causing her distress?

The brother has no right to prevent his sister from marrying someone suitable for her, and it is forbidden for him to obstruct her marriage. He must fear Allah, abandon his tribalistic zeal, and submit to Allah's command, just as happened with Ma'qil ibn Yasar. What the brother is doing is a forbidden obstruction of marriage ('adl), disobedience to parents ('uquq), and severing of kinship ties (qat' ar-rahim), and he must repent. If the father is present, he is the guardian (wali) of the girl and must marry her off without heeding the threats of the disobedient son. If he fails to do so, his guardianship falls, and the girl can raise her matter to the Sharia judge.