I have some info which may help in your quest. Robert was one of the two children of Edwin Holmes Van Deusen and Cynthia Ann Westover. His sister was Anna Margaret VD b.5/17/1862.
According to my info, Robert married Alys Betha Bates and then Harriet Louise Mosher on 6/6/1899. They, in turn had two children - Harriet b. 3/3/1900 and Robert Wendover VD b.1/27/1903.Descendants of Edwin Holmes Van Deusen
1 Edwin Holmes Van Deusen b: August 29, 1828 .. +Cynthia Ann Wendover b: August 04, 1835 ... 2  Robert Thompson Van Deusen b: April 26, 1859 in Kalamazoo, Mi. ....... +Alys Bertha Bates ... *2nd Wife of  Robert Thompson Van Deusen: ....... +Harriet Louise Mosher ........ 3 Harriet Huyck Van Deusen b: March 03, 1900 ........ 3 Robert Wendover Van Deusen b: January 27, 1903 ... 2 Anna Margaret Van Deusen b: May 17, 1862