Hmm... In my experience, they only repeated sibling names if the first one died, so two living Istváns have to be half-siblings at most.
Can you post a scan of that church document? It sounds like it's probably a birth register extract, but FamilySearch's indexed version doesn't say anything about the father:
https://familysearch.org/ark:/61903/1:1:X83X-676Istvan Prics
Hungary, Catholic Church Records
Name: Istvan Prics
Event Type: Baptism
Event Date: 15 Jan 1889
Event Place: Gelse, Zala, Hungary
Gender: Male
Mother's Name: Rozalia Prics
Line Number: 8 , GS Film number: 699786 , Digital Folder Number: 004499377 , Image Number: 00267