What are some advanced search strategies for German ancestors?
I am trying to find my German Ancestors. There is the Hoffmann family as well as the Boschen family. I've found immigration records for my great grandfather, Guenter Hoffmann and his spouse, Hanna (nee) Boschen, who immigrated to Australia in the 50's. Though, I cannot find any additional records about them, I'm not to worried since I've satisfied with knowledge i hold of them.
As for their parents, I cannot find anything, and all I have is their photos from my family photo album. Ages are estimated by assessing photos. My great grandfather was born in Friedland, but I'm unsure about his parents. (Oskar Hoffmann and Hedwig Hoffmann, estimated births 1896 and 1900.) Oskar Hoffmann, and his father Hermann, appear to have partipated in WWI, since I have a photo where they wear WWI military uniform. The Boschen's were born in Hengserholz, as far as I know.
I've found possible record matches but I cannot know for sure, because there is no immediate family attached to those records.
Ive done constant and deep searching for quite some time now online. Can anybody give me some advice?