Bensch, Zingel - Long lost German/Polish relatives

I'm looking for relatives of my great grandfather, Gustav Paul Bensch - born 27 May 1890 in Kozów, then Kosendau. He went by his middle name, Paul. He was married (don't know her name) and living in Jawor in 1929. He visited the U.S. in 1929 for an unknown reason and when he returned in 1933, his family was gone. Paul came back to the U.S. and remarried. He had a son, my still-alive grandpa, and I would love to find out if he has half-siblings out there.

A researcher from Legnica tracked down the birth certificate for Gustav Paul Bensch. His parents were listed as Wilhelm Bensch and Ernestine Zingel and they were evangelical. The researcher looked for birth records of siblings in the Legnica archive, but did not find any. My family does believe there were several brothers though.

Any information would be appreciated!

When looking for ancestors in former German territories, always use the German place names for research before WW2.

familysearch.org/search/catalog/results?count=20&placeId=49220&query=%2Bplace%3A%22Germany%2C%20Preu%C3%9Fen%2C%20Schlesien%2C%20Liegnitz%22

ezab.de/kirchenbuecher/kirchenbuch-suche.php?q=kibu/liegnitz.html