I read an article in the local paper (HNA) today of your search for information to link you to Johannes Wilhelm Siebert. Please contact me if you would like some professional help.
I have immegrated in the reverse direction.I left America in 1989 for Germany.I am an engineer working in R&D for B. Braun Melsungen, AG the 14th largest pharmiceutical firm in the world with headquarters in Melsungen, just a few miles from Spangenberg.I live in Felsberg, which is 7 miles to the west of Melsungen.My hobby as yours is genealogy.I have done extensive reasearch in Germany for my own family and for others.With 6 weeks worth of vacation every year,it is a good way to do research.
Can you read the old German script?This takes alot of practice and I was fortunate to meet friends who helped me.
In order to find descendents of Johannes Wilhelm Siebert one has to do the research in the church records and community property records.Likewise the asncesters of Johannes Wilhelm Siebert are probably traceable back until 1650.This should amount to another 4 generations.Have you done this research?