The 1940 census for ward 4, Jackson City, Jackson, MI has this family: HAMMER, Carl age 42 b. MI occupation salesman wife Gertrude age 35 b. MI son Hugh age 16 b. MI son Roland age 4 b. MI dau Carlene age 1 b. MI
In 1930 in Jackson there's a 30 yr old Carl HAMMER, widowed, listed as brother in the household of Irvin & Ferda DORMAN.
In 1920 in Jackson there is a 21 yr old Carl HAMMER and a 20 yr old Hazel HAMMER living in the household of Charles and Gladys THOMAN.Their relationship is not listed.
There's a marriage record for Carl F. HAMMER, age 21, to Hazel NELSON, age 20, on 17=Sept-1919 in Rives Junction, Jackson, MI.Groom's parents were Fred HAMMER and Cara GARFIELD.Bride's parents were Andrew NELSON and Alice CARPENTER.
I think it is likely that Hazel is Carl's first wife and the mother of Hugh.
1910 census for Rives, Jackson Co, MI: KILPATRICK, Clyde age 24 b. MI, both parents b. MI wife Cora B. age 34 b. MI, both parents b. MI son Harold D. age 4 son Erwin J. age 2 dau Margrett A. age 1y6m stepdau HAMER, Evelin V. age 13 stepson HAMER, Carl F. age 11 stepdau HAMER, Pearl E. age 10 stepdau HAMER, Lillie N. age 8 stepson HAMER, Fredrick D. age 7
1900 census, same location: HAMMER, Elizabeth b. Nov 1835 in Germany, 7 children born, 7 children living, widow, both parents b. Germany son Fred b. Nov 1872 in MI, married 3 yrs, both parents b. Germany dau-in-law Cora b. Oct 1875 in MI, 3 children born, 3 children living, both parents b. MI granddau Eva b. Mar 1897 grandson Carl b. June 1898 granddau Pearl b. July 1899
MI birth record for Carl F. HAMMER b. 19-June-1898 in Rives, Jackson Co, MI, son of Frederick and Cora HAMMER
MI death record for Fred D. HAMMER d. 22-Aug-1902 in Rives, Jackson, MI, son of Jacob HAMMER and Elizabeth HARMON.
MI birth record for Frederick HAMMER on 4-Nov-1872 in Jackson Co, son of Jacob and Elizabeth HAMMER.
1880 census for Rives, Jackson, MI: HAMMER, Jacob age 53 b. Germany wife Elizabeth age 45 b. Germany son Frank age 14 b. MI son Jacob age 12 b. MI dau Christina age 9 b. MI son Frederic age 7 b. MI dau Lizzie age 5 b. MI son John age 3 b. MI bro-in-law HUSER, Ludwig age 42 b. MI