We found your research on-line and though maybe you could assist us in our search.
Attached is a letter written by my husband's great-grandmother. It tells how their great grandfather was sired by Frederich Wilhelm III. I can't see that this could have been on the Duffelmeyer side, genealogy enclosed, it must have been another great-grandfather- on her side. I have no other info on the rest of this family tree and would also appreciate any info you might encounter. My husband's great grandfather is Clamor Heinrich Frederich Duffelmeyer listed at the bottom. He grew up in the house that I have attached a photo of.
I hope that this provides some clues that would be helpful.
Great thanks from us all!
Suzanne Duffelmeyer