Hi Armin,
There was an old family HATTORF which used the name OSTERODE too in the 14th
century in Braunschweig (=Brunswick) in Lower saxony.
This family probably came from the village Hattorf in the former county of
Grubenhagen nearby of the residence Osterode/Harz.
So perhaps you have to search in Braunschweig.
Greetings from Bremen!
Cord
Dr.med. Cord Winde
Bremen / Deutschland
e.mail: drwinde@aol.com