According to the book, "Gary, Garry, Geary, Etc.," p. 209, Andrew W. Gary was a younger brother of Harvey N. Gary, and consequently a son of James Henry Gary and Nancy Murry.Harvey was born in late 1838 and would have only been age 12 when Andrew was born in 1851, which is most unlikely.Andrew did have siblings Martha and Charlotte, but they, too, are children of James Henry Gary.
In the 1860 Census, he was living in the household of JH Gary in Newton Co., TX.
On July 1, 1874, Andrew W. Gary and Harvey N. Gary applied for Letters of Administration for the estate of their father, James H. Gary.Andrew was a resident of Panola Co. at that time.
Andrew W. Gary married 1)Sarah Manerva Williams 16 Feb 1870 in Panola Co., TX; he married 2) Martha J. Kinsey 2 Dec 1883 in Panola Co.; he married 3) Delia Camp 14 Aug 1901 in Panola Co.Following is what I have on his children:
Children by marriage to Sarah Williams: 1. Walter S. Reese Gary, b.Mar 1871, Gary, Panola Co.;d. 5 Mar 1916 Gary, Panola Co. 2. Susan A. Gary, b. ca 1872 3. Mary A. Gary, b. ca 1874 4. Henry Gary, b. ca. 1877 5. Minerva E. Gary, b. ca 1879 6. Lucretia Gary, b. April 1882
Children by marriage to Martha Kinsey: 7. Sidney A. Gary, b. Apr 1886 8. Ollie May Gary, b. Aug 1889, m. T. J. Moore 12 Apr 1916, Panola Co., TX 9. Earl T. Gary, b. Apr 1891
Children by marriage to Delia Camp: 10. Emory R. Gary, b. 12 Feb 1914, Carthage, Panola Co. 11. A. D. Gary, b. 16 Sep 1918
You indicated 10 children by his last wife, but I only have names for two.
A substantial portion of this info came from a fellow Gary researcher that I can put you in touch with, if you are interested.