Hello Yvonne,
I have sent your request to another mailing list too (AMF-list). I hope that anybody there can help you. Osterode, Einbeck and Lautenthal are in region Lower Saxony. I work in Langelsheim, near Lauthental and have searched for the name SEEGER in the phone book. But I couldn't find this surname in Lautenthal. May be that this family is transmigrated from this region.
Ok, wish you the best to get help from other explorers.
Jens Schumann from Goslar in Lower Saxony