Judy, things are now becoming a bit clearer. You posted here simply because you didn't realize who the Danube Swabians are. The "Ebberswald" mystery has also been cleared up. You are referring to the city of Eberswalde in Brandenburg after all.
Now we come to "Horstein". As was the case with "Ebberswald", there is no "Horstein" in Germany either. But again, there is a town that comes very close. That would be the town called Hörstein, or if written without the "Umlaut" (two dots) over the "o", Hoerstein.
Hörstein is located down in southern Germany in the state of Bavaria (in German: Bayern; capital: Munich), and to be precise, in the region of northwestern Bavaria known as Lower Franconia (in German: Unterfranken), the administrative seat of which is the city of Würzburg. Hörstein is no longer an independent town. In 1975, Hörstein was annexed by the nearby city of Alzenau. So today, Hörstein is a section of Alzenau. Alzenau in the Lower Franconia region of Bavaria is about 300 miles southwest of Eberswalde in Brandenburg.
The question is this: Does Hörstein sound like the town you're actually looking for?
One important thing, Judy: You've posted your query on two such obscure message boards -- the Germany Schleswig-Holstein board and the Danube Swabian board. It turns out that the Gruenwald family has nothing whatsoever to do with Schleswig-Holstein, and they have nothing whatsoever to do with the Danube Swabians. I really don't understand why you chose two such obscure message boards for your query. You won't get any useful replies from the two boards you chose. It was only by chance that I happened to see your queries myself.
I would strongly urge you to post your query again, but this time on the GERMANY GENERAL board, which is actually where you should have posted it to begin with.