What is the ruling on a person swearing an oath on the Mus'haf, disclosing the thefts committed by his brother and business partner, knowing that this oath will ruin his brother's future and cast him into the streets?

What was mentioned about your brother — regarding his ill-treatment, arrogance, and conceit — contradicts kinship ties, gentleness, and humility, all of which the Shari'ah has encouraged. As for his theft, it is a grave crime, and your duty is to advise him and pray for his guidance. Regarding his theft of the company's funds, if it is possible to recover them from him without exposing him, that is preferable. Otherwise, you must inform the company owners of what you know with certainty, or else you will be sinful.