Your grandfather seems to have been a first cousin to my late father-in-law.His name was Hilbert Ernst (02/25/1905 - 05/14/1976) and his father was Herman Frederick Rupnow (05/06/1870 - 08/15/1956) and his grandparents were the same.His grandparents names also were Frederick Christian Rupnow (12/10/1823-01/05/1913) & Caroline Hoeft Rupnow (05/11/1836-01/05/1916), as per the headstones at the cemetery.
Most of the information I have was by word of mouth from my father-in-law and his brothers.I was told that all of Christian & Carolines sons had the first name of Frederick but most of them went by their middle names.I have them as Frederick August, Frederick, Frederick Albert, and Frederick Herman, along with the sister Wilhelmine who was the one that did not immegrate to this country.She was married to an Otto Schroeder and I was told that they had one son (Paul) who died young.It is believed that he had a son, but nobody knew for sure.
I have some information on August's family which I got from one of his granddaughters.I have very little information on Frederick's family.I have quite a bit of information on FA (Albert's) family which I got from one of his granddaugheres.
I have extensive information on Herman's family as he was my husband's grandfather. He was married to Ida Bornfleth (05/14/1872-12/24/1932).They had nine children:Emil, Otto, Martin, Leonard, Edwin, Hilbert, Alex, Raymond, and an unnamed daughter that died at birth.Emil and his wife Leona Nell Rupnow had four children:Marvin, Howard, Melvin, and Harold.Otto and his wife Ilma Mueller had three children:Norman, Robert, and Linda.Martin and his wife Esther Korth did not have any biological children but raised Emil & Leona's youngest son from birth when she died in giving birth to him.Leonard and his wife Olga Sabatke had three children:Adeline, Alice and Harland.Edwin and his wife Clara Baker did not have any children.Hilbert and his wife Agnes Beneditz had nine children:Waldemar, Eugene, Allen, Marilyn, Karen, David, Ronald, Lawrence, and Hilbert.Alex and his wife Lydia Zastrow had two children:Rosalyn and Joanne.Raymond and his wife Dora Bienfang didn't have any children.I have names and dates of most of their children and grandchildren.
The Oak Grove cemetery has many Rupnows in it.Frederick Christian, Caroline Hoeft Rupnow, Frederick Albert, Emilie Mueller Rupnow, his first two babies, Herman Frederick Rupnow, Ida Bornfleth Rupnow, Hilbert Rupnow, Agnes Beneditz Rupnow, Waldemar Rupnow, Ronald Rupnow & his first grandchild, Frank Rupnow, Lydia Schujahn Rupnow, Clarence Rupnow, and Vilas Rupnow was just buried there yesterday.I'm probably forgetting some too.I get there quite often because my husband is buried there.
I have never checked any census records or immigration records, so that part of the records I am missing.