This is an amazing story and I will take some time soon to look at the archive that was created.
My father's family (in Germany their name was Konigsberger) was from Aachen and my mother's family (Herz and still Herz in the U.S.) lived in Dusseldorf. I will check to see if there is a Stadarchiv in these cities that might be of assistance. I would be happy with any help with transcriptions from the handwritten German letters into typed German. Currently, a German woman studying in the U.S. has been transcribing letters from my father into typed German and I have been using on-line language translating systems to turn them into English. The same with typed letters. However, most of the letters from relatives are handwritten because they were fleeing the Nazis and had no access to a typewriter. So far, even people whose native language is German and two relatives who are professors of German have been unable to decipher the handwriting of my grandparents and their generation.
In the future, I will write to you via private email.