Twin Mansions | William H. Vanderbilt Residences. Twin Brown Buildings -- 3 residences total -- 640 & 642 Fifth Ave, and 2 West 52nd St., NYC. Designed by John Butler Snook as homes for Mr. and Mrs. William H. Vanderbilt I and daughters Emily Vanderbilt [Mrs. William Douglas] Sloane and Margaret Vanderbilt [Mrs. Elliott Fitch] Shepard. 640 Fifth Ave. was later the residence of Capt. and Mrs. [Grace Wilson] Cornelius Vanderbilt III.
Petit Chateau was a Châteauesque mansion at 660 Fifth Avenue on the Upper East Side in New York City. It was built for William Kissam Vanderbilt & Alva Vanderbilt from 1878 to 1882. Determined to make her mark in New York society, Alva Vanderbilt worked with the architect, Richard Morris Hunt, to create the French Renaissance-style chateau. It was sold to a real-estate developer in 1926 & demolished. In a draft of her memoirs, Alva, then Mrs. Belmont, merely noted the demolition in passing.
Cornelius Vanderbilt II purchased and demolished 3 brownstone houses on the southwest corner of 57th Street and 5th Avenue in preparation for his new mansion. Description from pinterest.com. I searched for this on bing.com/images