Mary Ellen O'Shaughnessey

I am looking for records in Ireland for the family of Terrance O'Brien and Mary Ellen O'Shaughnessey, and their children Daniel, Thomas and Catherine.  Presumably Terrance and Mary Ellen were married between 1815 and 1825.  Estimated dates of birth are below.  We think they were from county Cork or Limerick.  All the information below is from records in Canada, where they came sometime before the 1851 census.

Religion: Church of Rome, Roman Catholic

Occupations:
Terrance: mason
Daniel: mason
Thomas: joiner
There is a family story passed down that they worked on the Canadian parliament buildings.  This could be true, since they lived in Ottawa/Carleton in 1861 (see census below) and the parliament buildings were officially opened June 6, 1866.
https://www.thecanadianencyclopedia.ca/en/article/parliament-buildings

Terrance and Mary Ellen are listed as the parents of Daniel O'Brien when he married Rose (Rosalie) Neville in 1853 in Quebec City. The document is in French, so Helene in the document is thought to be the translation for Ellen.
This document was found on Ancestry:
Marriage date: 1853
Marriage place: Lévis (Notre-Dame-de-la-Victoire), Québec
http://search.ancestry.com/cgi-bin/sse.dll?db=drouinvitals&h=12432086&ti=0&indiv=try&gss=pt
The document also states that Thomas O'Brien, the brother of Daniel, was a witness and signed the document.

It is also believed that Terrance and Mary Ellen had a daughter named Catherine. A Catherine O'Brien is listed as signing as a witness for the baptism of Daniel and Rose's oldest child, Thomas, in 1854.
This document was also found on Ancestry:
Birth date: abt 1854 Birth place: Québec Baptism date: 1854 Baptism place: Lévis (Notre-Dame-de-la-Victoire), Québec
http://search.ancestry.ca/cgi-bin/sse.dll?db=drouinvitals&h=774012&ti=5543&indiv=try&gss=pt

The Canada censuses for this family are in Quebec City and Ottawa Carleton and can be found at Library and Archives Canada website. They are difficult to read, but the following are thought to be the ages listed for the family members:
(Note that the 1851 census of Lower Canada, i.e. Quebec, was actually done in 1852)
Terrance (age 59 in 1852; died at age 65 in 1860 as documented on the 1861 census; thus birth between 1793 and 1795)
Mary Ellen (age 54 in 1852; age 60 in 1861; thus birth between 1798 and 1801)
Daniel (age 26 in 1852; age 35 in 1861; thus birth about 1826)
Thomas (age 21 in 1852; age 30 in 1861; thus birth about 1831)
Catherine (age 15 in 1852; age 26 in 1861; thus birth between 1835 and 1837)

1851 census in Quebec City (taken in 1852)
The information page:
https://www.bac-lac.gc.ca/eng/census/1851/Pages/item.aspx?itemid=1076886
The first page of this self-filled census looks like it was filled in by Daniel, since it has the same handwriting as Daniel's signature in the marriage and birth records listed above.
https://central.bac-lac.gc.ca/.item/?app=Census1851&op=&img&id=e002330135
The second page was signed by Terrance O'Brien
https://central.bac-lac.gc.ca/.item/?app=Census1851&op=&img&id=e002330136

1861 census
https://central.bac-lac.gc.ca/.item/?app=Census1861&op=&img&id=4108498_00773
shows Daniel as head of the house and Mary Ellen as his mother being age 60.