I happen to have a genealogy book for persons living in the Bischmisheim area of Germany before 1900. There are quite a few NEMENICH listed. Even though the spelling is a little different than NEMNICH, you might want to have me check on your german ancestors to see if they are listed in the book. The oldest names in the book are these:
NEMENICH, Johann Christian, from St.Arnual.Occ: Day Laborer ..b.abt 1787 in Gunspach; died 28 Jan 1844 in Bischmisheim He was son of Valentin NEMENICH and Anna SCHWARTZ. Johann married on 13 Jan 1819 in Bischmisheim, to Magdalena WAGNER.
Their children: 1. Catherina b.August 1819 St.Arnual; d.16 Feb 1822 Bischmisheim; she died of emaciation. 2. Christian b.10 Feb 1821 St.Arnual; m. Catherine Elizabeth ANHAUS in 1849 3. Phillip b.01 Dec 1823 Bischmisheim; m. Maria Magdalena SCHNEIDER in 1853 4. Wilhelm b.27 June 1830 Bischmisheim; died 01 April 1831 5. Magdalena Carolina b.19 Sept 1833 Bischmisheim; living with someone (not married) in 1856; married Frederich Jacob SCHNEIDER on 09 April 1865 6. Catherina b.18 Sept 1836 in Bischmisheim
Let me know if any of this sounds familiar or you want me to check on your ancestors in Germany to see if they are listed in this book.