Is it permissible to refuse housing for a morally corrupt, addicted brother who harms and threatens his family, out of fear of his harm, relapse, and negative impact on the family?

Your brother is disobedient to his Lord and negligent in the rights of his family due to his drug use, disobedience to parents, and severing of kinship ties. We advise you to supplicate for his guidance. If you are tenants of the house, there is no sin upon you in preventing him from living with you if harm is feared from him. Obedience to your mother in commanding you to allow him to live with you is not obligatory in this situation. However, if no harm is feared from him and his living there serves an interest for the parents, then obedience is apparently obligatory, and you should not rush to refuse his living there, especially with the hope of his repentance after rehabilitation.