Blackstone Group and Fairstead Capital quietly sold an 18-story Kips Bay rental building to Adam and Aaron Daniels’ A.D. Real Estate Investors for $52 million, sources told The Real Deal. Since the firms paid $690 million for the Caiola family’s 24-building Manhattan multifamily portfolio in 2015, they have quietly looked to sell at least a few of the properties, despite frequently touting their multifamily investments as long-term plays.