For the Balkan Wars
Hall, Richard (2000)The Balkan Wars 1912-1913: Prelude to the First World War (Warfare and History)
Hooton, Edward Robert (2014)Prelude to the First World War: The Balkan Wars 1912-1913
Erickson, Edward(2003)Defeat in Detail: The Ottoman Army in the Balkans, 1912-1913
The Osprey book is also a good intro.
For the Balkan Front in WW1
Lyon, James (2015)Serbia and the Balkan Front, 1914: The Outbreak of the Great War
For Austria
Schindler, John (2015)Fall of the Double Eagle: The Battle for Galicia and the Demise of Austria-Hungary
Gumz (2009)The Resurrection and Collapse of Empire in Habsburg Serbia, 1914-1918: Volume 1
DiNardo (2015)Invasion: The Conquest of Serbia, 1915
Hall (1996)Bulgaria's Road to the First World War