I also have family that settled in Jersey City. I've been able to track most of them, but it took time and effort. The family name was so mangled by census takers that it was hard to find them.
Have you tried the Searchable Death and Marriages databases at the New Jersey State Archives? http://www.nj.gov/state/archives/searchdatabases.html
Their server seems to be down this morning or I would have looked there for you.
Do you know their religion? Jersey City Catholic records on microfilm from Salt Lake were enormously helpful in my search. You can borrow the films and view them at your local library or Family History Center, depending on your location.
And, finally, I hired a researcher to go to the Archives in Trenton to retrieve documents. There are some indexes available there that are not online, and he was able to locate several items for me. Contact me offline if you are interested and I can give you contact information or a list to choose from.
I'm still missing one critical member of the family - my 2xg grandfather, Thomas Holleran. I would also like to find out more about the oldest child, John Holleran. I've located my GGM and her 3 sisters.