Can the evil eye or sorcery deprive a person of sustenance, work, health, and marriage?

Slandering your brother for the sake of Allah the Almighty is an act of disbelief that expels one from the fold of Islam, and sincere repentance is obligatory upon him. The problems you are facing may have tangible causes that require practical solutions, or they may be due to magic (sihr) or the evil eye (ayn), both of which are real and have a proven effect in Islamic law. For protection and treatment, one should seek out tangible causes, fortify oneself with ruqyah ash-shar'iyyah (Islamic incantations) and established supplications, and changing one's place of residence might be beneficial. It is advisable to counsel your brother on the necessity of repentance and returning to Allah.