Your brother does not need the consent of his spouse to file for divorce. If she has abandoned the marital home for over one year, he has grounds for divorce and may file a summons and complaint for divorce under New York State law.
If they are living in the New York City metropolitan area, I strongly suggest that they call me at 212-370-1660 to discuss mediating the divorce as opposed to litigating it in the court. It is quicker, cheaper, and less emotionally straining.
Leonard M. Weiner, Esq./Divorce Solutions