Hi Jozef, I do know John Schwarz, we are connected through the Hein/Heine family. I didn't know about Potsdam Archive so thankyou for that information.
I have found the births of J.G.& Caroline/Karoline Hein/Heine's 6 children in Preussen, 1875 - 1882. Some are registered as HEIN, some HEINE.
Thankyou for your help ...........Sashar