I could not find Gerhard but I have the 2 sisters listed, Barbara born 28 Oct 1867 and married Johann Penner on 21 Mar 1889 - they had 9 children.Her parents are listed as Nikolia Harder and Gerturde Wiens.
Not connected but also on the data base is Gertruda Harder born 1 Feb 1870 who married Heinrich Aron Weis born abt aug 22 1862 and died in 1933 (doesn't say where)they appear to have had one child Gerhard Weis.
Looks like no one has put the three family members together if indeed these three are connected. What was your grandmothers maiden name and your grandpa's exact birthdate?
Anything of interest here??
Cheers Ron (you can email me direct at firstname.lastname@example.org)