How can one advise a brother who is entrusting the management of his company to two men known for their profligacy and moral corruption, and will that affect the blessings of the company's income?

If the men who manage your brother's company do not engage in forbidden financial transactions through their management, but rather their problem lies in their فسق (open transgression/disobedience to God), then employing them is not haram. This is because it is permissible to hire a disbeliever, let alone a fasiq (transgressor), just as it is permissible to engage in business partnerships with such individuals. However, it is preferable to choose employees who possess good character, piety, and trustworthiness.

As for companionship and socializing, interacting with such individuals, even if it does no harm, will not bring benefit. And sitting with someone who openly commits sins is harmful.

Your brother must enjoin them to good and forbid them from evil, and invite them to righteousness. If they persist in their state, then it is better to replace them with others who are righteous, upright, competent, and trustworthy, so that he does not aid them in their transgressions. For whoever strives against them with his hand, or his tongue, or his heart, he is a believer, and changing evil is an obligation.

Abundance of wealth and increased profits, if deprived of blessing, will not benefit their owner, and sins are a cause for the eradication of blessing.