The three Elghanayan brothers who own Rockrose Development Corporation, a residential and commercial developer, are splitting the firm into two, Crain’s New York Business reported. The reasons for the separation and the way Rockrose’s properties will be divided are not yet clear, according to sources close to the situation. The oldest Elghanayan brother, Henry, will keep the Rockrose name and move to a new office at 666 Fifth Avenue. The other two brothers, Thomas and Fredrick, will continue to work together at a company expected to be called TF Cornerstone, which will continue to operate out of the company’s 290 Park Avenue South headquarters. Rockrose is currently developing a 22-acre project in Long Island City, Queens, and several condominium and office projects in Manhattan.