I am hitting a brick wall with my great great grandparents Anna and Albert Oldenburg. Anna was born 9 Jan 1875 in Falkenburg, Germany. On her death certificate it lists a Frederick Russ as her father, but no mother. The information was provided by a neighbor. The ship manifest lists her husband Alberts brother in law as a Josef Koenig. Searches with Russ and Koenig bring up nothing. Albert Oldenburg was born 24 OCT 1873 in Diersdorf, Germany. He married Anna in Berlin Germany in 1904. Their children were Walter, Willy, Kaeth (Kathryn), Hans, and Charlotte. All the children were born in Berlin. They came to the US in 1923. I have one census listing the parents and children, and one census listing only Anna and Albert in their later years, both census they lived in Fond Du Lac, Wisconsin. I have the ship manifest (Canopic) and I have the naturalization petitions. With all the information I do have, I still come up empty. I was hoping someone could help me get past this brick wall. I feel like I have wrong information somewhere or I am overlooking something. Having Anna's maiden name would help a lot. I have checked Familysearch.org and find nothing there other than the naturalization records. Thank you for the help.