I cannot see the attachment you posted above. If you have any document you think could help narrow this down, email it to my address: email@example.com
Zoroja surname could be both, a Croat or Serb. What was Petar’s and Jillian’s religion? That is the easiest way to distinct Croats (Catholic) from Serbs (Eastern Orthodox). Also he may have been a Serb from Croatia (most of the Serbs in the USA are originated from the parts of Croatia populated with that minority).