Nash Family

I have limited information about my Irish ancestors. I do know from a death cert that James B Nash was from Limerick...not sure if that's the city or the county. James B Nash (b. 1817) married Margret Johnston (b. 1813 Scotland?)  in 1837 I believe in Ireland where son James T Nash was b 1841. Looks like they immigrated to Canada/US where the Quebec church records show baptisms for Mary b. 1843, Richard & Peter (possible twins) b. 1853. Other children born in Vermont--Robert 1845, Thomas 1847, Michael 1854. Then a few born in Minnesota John 1858, Margret 1860.  Margret died in St Paul in  Nov 1884 at home from a stroke and James died a month later getting hit by a train in St Paul. Some say due to excessive grief and was just not paying attention.

I know Patrick was James brother. He was a contractor in St Paul MN that helped establish the sewer system. There was at one time a street named NASH in St Paul but has now been changed. The old City Directories do show this street. Patrick (b 1814)  married Johanna Seahnan (b 1817) in Ireland sometime before 1833 when their son, William, was born followed by their daughter Mary b 1842. They too came to Canada where Johanna b 1845, Bridget b 1848 and John b 1851 all are shown in the Quebec church records. Other children born in Minnesota Baby Nash b.1856 d 1856 in St Paul, William b 1859 d. 1860 in St Paul. 

Possibly the father of Patrick and James is Joseph Nash but have not been able to confirm this. I have not seen in any Irish records on Ancestry this family unit in/around 1820 when they would have been children. Since these names are very prevenlant in Irish society not sure how to locate MY Nash family. Any ideas, thoughts, areas of interetest, would be greatly appreciated.