"For now, I will assume the Dusan born in 1935 is a son and the Dusan born in 1900 to be the father who was killed in the war. "
I am afraid that your assumption is wrong. Name of the father is listed for this boy - it is RANKO.
Also, ethnic Serbs traditionally almost never named a son after their father - except in special circumstances, as an *ultimate* protective name after losing (many) children at an early age, especially sons.
If you are going to make any assumptions, then the assumptions should be according to the naming customs and patterns exactly the opposite - that DUŠAN was in most cases not the son of a DUŠAN.
These are the only two people from Sremska Mitrovica municipality who were killed in war with first name DUŠAN and surname resembling the ones you posted of adequate age :
Stanišić (Jovan) Dušan,
ubijen od ustaša 1942. u masovnom pokolju u Sremskoj mitrovici
He was from the village LEŽIMIR
Stanković (Gliša) Dušan,
umro 1942. na prinudnom radu, Bijeljina
He was from the village SREMSKA RAČA
Surname ORLOVIĆ was present in the village LEŽIMIR.
Serbian Genealogy Society SGS "Rodoslovlje"http://www.rodoslovlje.com/en