it would be helpful if you could send us a scan of the image that says Leimerwitz.
To get Hans’ birth certificate from Racibórz, you need to write to the state archive in Racibórz.
Give them these two file numbers: 18/282/0/1/37 18/282/0/1/38
and as much information as you have on the family (names, date of birth, etc.).
Contact information: https://www.katowice.ap.gov.pl/p,74,raciborz
Mind that the surname Sikora was also spelled Schikora in many places.
If they came from Leimerwitz, they should appear in this database: http://www.online-ofb.de/nassiedel/index.php?lang=en
You can navigate it by clicking on “Complete List of Surnames” on the left.
The database does have some entries for Sikora and Schikora.