Patrick O'Meara & Wife Catherine Howe - Child Stephen born Rapla

My family history is that of Patrick O'Meara born 1789 in Ireland and died around 1853 in Canada and his wife, Catherine Howe born about 1788 in Ireland and died in 1867 in Canada.  They emigrated in 1847 to Canada (another report conflicts and says 1845) and were reportedly the parents of 9 children, their son, Stephen O'Meara born in 1832 in Rapla, Nenagh (per obit), and was their 7th child out of the 9 (per research from Canada). Two younger brothers I've been able to find proof of their relation to the family were that of Hugh O'Meara b. 1835 in Tipperary and that of James O'Meara b. 1837 in Tipperary.  Hugh was in Canada for a while, then moved to Detroit, Michigan before eventually moving back to Canada.  He died in Canada, but before that time his wife and children all move to New York where all of his remaining family dies.  James moved around a bit throughout the USA, and lived for a time in Illinois, but was mostly in Missouri before his children died and he wound up being widowed.  He eventually moves back to Canada and dies there.

I have had a difficult time determining who the other 6 children might be to Patrick O'Meara and Catherine Howe.  I believe I have identified 2 other boys though.  One would be that of my 2x gr grandfather John O'Meara b. about 1823 in Tipperary and dies in Canada in 1886. The second being that of Dennis O'Meara b. 1830 in Tipperary and married in New York before living in Rutland Co., Vermont and eventually moving and dying in Rhode Island.

Is there a recommendation that could be given that could possibly further confirm the 2 boys (John & Dennis) and who the additional 4 missing children might be?  I would prefer to look through parish records myself, if available, via the USA.  Where would one begin to look at such an early time frame?

I appreciate any input anyone might be able to provide.

Sincerely,

Susan O'Meara