I should have posted this in March, but better late than never.
The German translator came through and we now have more information about Hermann's parents, including something unexpected. Here are the highlights:
Hermann Ringel's birth record shows he was born November 5, 1885 in Berlin, that his parents were Schija Ringel and Feigel Kaufler. Kaufler was Ringel's unmarried Jewish housekeeper. A notation on the birth record from two and a half years later indicates that Schija and Feigel married on July 2, 1888.
Feigel's death certificate from November 28, 1921 (three years before her granddaughter Helga's birth), describes her as 67 years old, a shopkeeper, born in Krakow and residing at the same address in Lothringstrasse as her son Hermann.
Hermann's death record from June 25, 1938 is pretty spare, and does not appear to tell us anything new.