It would help to know more about where in the US the families you mentioned settled. The more information you have found in the US, the easier it is to verify and get information in Germany or other foreign countries. Get names, dates, places, as much as possible.
In checking family trees and your previous e-mails it seems you are a descendant of Carl Wilhelm Manthei from Para, Jackson, MI. Have you found his emigration record (ship passengers list, citizenship application, etc.)? Census records indicate it was 1891 or 1892 when he came. What about his brothers and sisters too?
Do you know Ludwig's place of death? Obituary? Anything there would help.
Kreis Schlochau is in West Prussia, and Rosenfelde is next to Kreis Flatow where many of my relatives resided at various points.
All the best,