In 2012, 2 former Bremen co-singers, Daniela Witt and Gunnar Heite, made a documentary about the early years of Sacred Harp Bremen. This film gives a wonderful picture of how the Sacred Harp tradition landed in Germany and how the group in Bremen has come into being and grown since that time.
Due to illness of the makers, this documentary has been a long time coming, but now the full version is finally available on Youtube. The film is German spoken and has English subtitles. See the link below: