From his patronymic as seen on JRI, it would appear that he was a son of his 'brother' Zvi Hirsch Ozer Zausmer and thus a grandson, not a son, of R' Menachem Nahum Zausmer of Bialystok - who ought to have had only 2 sons, incidentally.
From his patronymic as seen on JRI, it would appear that he was a son of his 'brother' Zvi Hirsch Ozer Zausmer and thus a grandson, not a son, of R' Menachem Nahum Zausmer of Bialystok - who ought to have had only 2 sons, incidentally.
Sure. 1892 Bialystok marriages, akt 58
CAUZMER, SaulZigfrid Gerszowicz 1892 M 58
ZABLUDOWSKA, Fanni Gustawowna 1892 M 58
(A scan of the original is here, in Russian: https://www.szukajwarchiwach.gov.pl/skan/-/skan/d11918967fd21abc4d7...)
The first Cauzmer/Zausmer in Bialystok was R' Menachem Nahum Zausmer of Bialystok, so 'Gersz' cannot be his father, so must be his son, and Saul-Zigfrid, his grandson.
That marriage is for Saul Zigfrid Cauzmer and Fanny Cauzmer.
You need to look to see if you can find anything on the current siblings of Saul.
Kevin
I also have a source from the 1920s who seems confident that R' Menachem Nahum Zausmer of Bialystok only had two sons, Zvi Hirsch Ozer Zausmer and Oszer Enzel Cauzmer.
(See Avot Atarah la-Banim, a classic genealogical reference work, digital pages 222, 223, 246: https://hebrewbooks.org/pdfpager.aspx?req=46893&pgnum=222 )
I'd say that Zvi Hirsch Ozer Zausmer's son Saul Zigfrid Cauzmer is a duplicate of Saul Zigfrid Cauzmer, only with the correct father. (the information there is based on the same source linked above)