George Bernard was married. His wife was Julia Anna (or Juliana) Schroeder. They were married circa 1867 in Cincinnati. (Cincinnati vital records for that time period were destroyed in a...wait for it... courthouse fire!)
Their children are:
Henry A. Knoppe (b. 1870 / m. Sophia L. James in 1899 / d. 30 Dec 1934)
Anna Marie Knoppe (b. 1871 / m. Edward Zoller in 1891 / d. 28 Nov 1942)
Louis Ludwig Knoppe (b. 1874 / d. 24 Apr 1884)
George Bernard Knoppe Jr. (b. 31 Jan 1876 / m. May Rose Marie Hoffman 26 Jan 1909 / d. 16 Mar 1939)
Ella Knoppe (b. 8 Apr 1878 / m. Arthur Chester Paul 19 Jan 1904 / d. 19 Dec 1956)
Mary J. Knoppe (b. Aug 1880 / d. 18 Apr 1956)
Benjamin Knoppe (b. Jul 1882 / d. ?) Unverified child
Bernard Knoppe (b. 5 Jul 1882 / m. Bertha C. Haverkos in 1911 / d. ?) Possibly Bernard and Benjamin are the same person, or twins, I don't know.
Charles Louis Knoppe (b. 17 Aug 1884 / m. Rose Burns / d. 20 Jun 1935)
Edward Theodore Knoppe (b. 19 Aug 1888 / m. Hilda Gentsheimer / d. 8 Aug 1946)
I do not know of any siblings that George had. There is another Knoppe / Knobbe listed in the 1869 Cincinnati Directory (the earliest I have found that mentions him) by the name of Lena, but I have been so far unable to determine whether there is any actual relationship.