East Germany is probably run by the Soviets the same as OTL. The only difference TTL is that Germans would be fleeing eastwards from the West instead of vice versa.
It doesn't make sense for the Soviets to ethnically cleanse East Germany. All the Germans expelled from the Sudetenland and east...
Check out Twilight of the Red Tsar by Napoleon IV. POD is Stalin surviving his stroke and living for another few years.
Edit: I realise that I misunderstood your comment. Stalin surviving his stroke would still be the main POD since it would mean prolonging the Doctor's Plot/Second Holocaust.
He was last mentioned in Chapter 2088. His father-in-law secretly sent him to America under a false name, only for him to commit a crime and be deported back to Germany where Kat could reach him.
Minor nitpick: Kingisepp would still be named Yamburg TTL, the renaming only took place in 1922, and with Lenin in charge.
(No, I'm no maestro of place names, I just Google them if I don't know them)