Why did the kaiser of Germany and the emperor of Austria-Hungary abdicate after the end of WW1? I know that the allies wanted to convict them of starting the war but couldent they just pass the thrones to their Heirs rather then abolishing the monarchy?
I'm not informed on Franz Josef I, but I can answer for Wilhelm II! - I answered a similar question on his exile earlier.
On the 10th of November 1918, Kaiser Wilhelm II boarded a train of seven carriages to the neutral Netherlands, he settled first in a small village in the Utrecht province of the central Netherlands, this was where he issued his statement of abdication of the Prussian throne, as well as that of imperial Germany.
Wilhelm then purchased a country home, in Huis Doorn and moved there on May 15th 1920, following this, he was granted the right to move some 63 carriages of his belongings from his previous palace in Potsdam by the newly created Wiemar Republic.
In his memoirs, published in 1922, Wilhelm distances himself having any role in inciting war as well as defending his record of leading Germany. - He refused any real responsibility.
Sources: Weinert, Christoph (2007), Wilhelm II. – Die letzten Tage des Deutschen Kaiserreichs [William II – The last days of the German Monarchy]
The American Year Book: A Record of Events and Progress. 1919.
Hohenzolern, William II (1922), My Memoirs: 1878–1918, London: Cassell & Co, Google Books.
Macdonogh (2001), The Last Kaiser: William the Impetuous, London: Weidenfeld & Nicolson
"William II. of Germany". Encyclopædia Britannica (11th ed.). 1911.
http://www.huisdoorn.nl/en/visitors/opening-times-prices/
(I probably forgot to include a fair number, I've lost them, so sorry!)