Perhaps you can share more info about your Nicholas (Nikola or Miko in Croatian)
1)what is his birthdate (as you know it)
2)Did he emigrate from Croatia?
3)If he emigrated where did he settle?
4)what was the name of his spouse?
5) what are the names of his children?
6)when did he pass?
7) what was his religion?
I take heritage groups to Croatia every year and have done a great deal of research at churches as well as the State Archives. We have also become very successful at conecting travelers with living family.
There are only a very few men in US records with this name.
Croatian Heritage Museum