Help with research

[MiKa73]

In baptism record of Karl Hermann, his father's name was - Max Schön, and mother's name was - Wilhelmine Goik.

But their full names was Wilhelm Max Schön and Auguste Wilhelmine Goik.

They were married in 1902.
Here is a civil marriage record of Wilhelm Max and Auguste Wilhelmine:

Page 1
https://photos.szukajwarchiwach.gov.pl/ ... d7f4dd_max

Page 2
https://photos.szukajwarchiwach.gov.pl/ ... 05fc83_max

Krzysiek

Hello, I try to continue my research and I would like to find if "Karl Hermann SCHON" has brothers and sisters?
How to search?
Thank you.