All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.
If you are sure that your brother is actually homosexual, we advise you to supplicate Alalah for him. Verily, a sincere supplication for one’s fellow Muslims is accepted as reported in authentic Ahaadeeth. You should eagerly advise him, even indirectly. You may make him listen to religious lectures about that issue and urge him to get married. Please refer to Fataawa 90562, and 89844 about the possible means to accomplish this objective.
Also, we have highlighted in Fatwa 86090 that the consideration of interests is the basic criterion for resorting to forsaking, or cutting relations with, one’s fellow Muslim.
Finally, if your brother persistently continues to engage in homosexual activities, after taking the aforementioned steps, you may threaten to inform those people who can deter him from doing this evil. You may actually inform them, if necessary, in order to correct him and deter him from committing that grave sin. It should be noted that you are not obliged to leave the house in which he lives unless you fear for yourself any harm (by staying with him).
Allaah Knows best.