Julianna would be spelled Juliana (no double consonants nor double vowels in Croatian) Julie would be Jula. J has a y sound.
Nickolas is not a Croatian spelling it should be Nikola.
Have you actually found a ship manifest for him?
I believe I have mentioned before that we had a lady whose greatgrand.ather was Nikola NOVOGRADAC and he married a SESTRIC, as found in Johnstown PA (Cambria County marriage records). I have found an 1895 arrival for a Nikola NOVOGRADAC destination Johnstown PA As I was doing some research on the PA NOVOGRADAC and SESTRIC I kept running into info on your family in KC.
The only male NOVOGRADAC I find going to KC is a Mijo, whose age is about right for your Nikola
There are records online but they only go up to the mid 18702 but may show the birth of Juliana and Izidor. They are in Latin and can be found at https://familysearch.org/search/image/index#uri=https%3A%2F%...
Otherwise I have a genealogist friend who has info on the parish. If you are interested in contacting him and/or if you want to be added to my mailing list please email me at email@example.com
Croatian Heritage Museum