I don’t know about Jernej Zetko being Frank’s brother. It certainly looks like a possibility, as they are from the same place – Senosec, Austria.
I have recorded the results of my Zetko research at familysearch.org. You can register for free there and see the sources I found. Just go to familysearch.org, register, and go to Family Tree. Click on “Find,” and search for Frank Zetko (1873-1920), whose ID number is LDCM-X6J.
My daughter-in-law is the granddaughter of the Frank Zetko who lived 1908 – 1988, and his brother is Joe Zetko. Their father was the Frank Zetko who immigrated from Austria/Slovenia/Yugoslavia (It varied what country had jurisdiction over the years.) I suspect that the Frank Zetko who came in 1905 on the Getty is this person, since he lists Senosec as his last residence. His wife and daughter Paulina made a voyage in 1930, and the daughter lists Senosecchia as her birthplace. I have learned that Senocecchia is the same as Senocece, which is probably also the same as Senosec. His age, however, is off by about 5 years compared to the age given in the 1920 Census and the 1911 immigration.
Frank Zetko (1873 – 1920) lists 1911 as his immigration year in the 1920 census, but I think there were several voyages. Their first son, Antonio, was born in Brazil in 1906, then Frank Jr. in Austria (1908), Paulina (1910) in Senocecchia. Joe and John of course were born in the U.S.
You will see at familysearch.org that Luca or Luka Zetko is the father of the first Frank Zetko, as that name is listed in the 1911 immigration record.