Hi Steven, Germany as we think of it as a country did not exist at the time period you are asking about. Do you know if they spoke what is called
High German, Low German, or PlatDutch? That can help identify where to look.
There are a lot of people with the same names in the same time periods in close areas so you need more to make a verifiable match to your family.
Now, this may sound really odd, but, are there any family specific recipes that came from your great grandparents that have been handed down? Sometimes recipes are more regional and can point you to a place to look. I have been able to track down a few people because of what they ate or did not eat. (Example people with an allergy to onion seem to have ancestry from a specific area of what we call today Germany and Austria. like my business partner and yes, she has that allergy).
In my case, my great great grandfather who descended from glass and crystal makers was a candy maker... the economy had bottomed out for glass makers when pressed glass came in and some famous candy making names came from glass families because it was chemistry... swap out the sand for sugar, the potash for flavoring or color and you have candy. Ribbon candy is made like ribbon glass, lollipops are stained glass windows, taffy is pulled and can be shaped just like glass. The tools look remarkably the same from the 1800s. Yep, sometimes occupations can also be a great help in sourcing people's past.