It took me the longest time to find the parents of my great grandfather, Johann August Fredrich. I found the names of his parents by researching his sisters that were named in his obituary.
The above death certificate is for Amalie (Fredrich) Engelhuber, J. August's sister. The informant was Amalie's daughter, Mrs. Charles Schoedel, Mae. The parents are listed as John Fredrich and Susana Koenig. The baptismal records of the children list the parents as Christoph Fredrich and Susanna Koenig. I am guessing the father might have been Johann Christoph, but until I see proof of that I use Christoph.
Amalie Fredrich was born 14 June 1842 in Prussia. She married Leonard Engelhuber on 27 January 1873, in Manistee, Michigan. Her death was 24th December 1930, in Saginaw, Michigan.
Don't rule out siblings when researching your ancestor, you may find what you have been searching for through one of the siblings.