I was in Dresden two weeks ago and bought Prince Ernst Heinrich's memoirs "Mein Lebensweg. Vom Königsschloss zum Bauernhof.", which I can highly recommend. Lots of interesting anecdotes and interesting perspectives on Germany history from pre-WW1 to WW2. He was not only close to many key players during the monarchy, but also during the Weimar Republic. Some interesting titbits:
His eldest brother, Crown Prince Georg, who became a monk and probably was murdered by the Nazis, was called Jury en famille, because he, just like his father, had a Sorbian nanny. The Sorbian he learned from her probably also helped him learn Polish.
A few years before WW1 the RF was besieged in the palace in Dresden for three days due to Socialist demonstrations of unemployed workers.
The planned German spring offensive on the Western Front in 1918 failed partially (according to the Prince) because the supreme command deemed it impossible to let Crown Prince Rupprecht of Bavaria and the troops under his command play their planned key part instead of German Crown Prince Wilhelm. Neither was Crown Prince Rupprecht's offer to let Crown Prince Wilhelm take his position deemed dignified enough by the supreme command.
It was custom among the German royals (at least from reigning families) to adress each other with Du, although younger royals often added Onkel (and presumably Tante for women) when adressing their seniors, even though they were not directly related. Emperor Wilhelm II, though, preferred that other non-reigning royals adress him with Sie or Majestät.
In 1918 Prince Ernst Heinrich was sent on a diplomatic mission to Estonia and Finland. In Pskov he met the local metropolitan bishop who had councelled NII during his abdication (and advised him not to abdicate) and in Finland the government ferried him around in the IF's former Imperial train, which made a deep, eerie impression on him (as his father had told him about the very friendly reception he had gotten from NII during a state visit to Russia and the train staff told him about the grand duchesses running in the corridors) and he knelt down in prayer in front of the imperial icon still hanging on the wall.