Looking for grtgrtgrandparents

Hi,

I have a copy of my Great Grandparents marriage certificate their names are Christopher and
Julia Galbraith. They got married at the church of SS.Michael &
John RC on 17 October 1869 and I believe they lived at 14 Fishamble Street
South Dublin and his father's name was James Bergin, occupation
was a (Silver Plater)
                    
On the certificate that I have purchased it just states ages so I have
an idea that he was born about 1848.

I have seen a Griffith Valuation of a 'James Bergin' living at
42 Wicklow Street, St Annes and could well be my Great Great Grandfather   

I was hoping somebody could help with some info, as I have hit a brick wall
trying to find or make a connection with my Great Grandparents
and my Great Great Grandparents.

I have been on a few Geneology sites but it appears that they
have not been updated before 1848. But I understand that the BMD documments
where destroyed in 1922.

In 1870 my Great Grandparents had a Daughter named 'Elizabeth Bergan' (different spelling) born at
19 Bride Street on 31st March and was Baptized on 11th April at
St Nicholas church RC.

After Elizabeth was born in Ireland my Great Grandparents had 5 other children who were all
born in Liverpool England (1872 Mary Jane) (1874 James) I have also
noticed in the Liverpool Catholic Baptisms that James's Godmother was called
Mary Donohoe, (1875 Christopher),(1878 Joseph Patrick) and (1880 Patrick - My Grandfather)

My Great Grand mother died in 1880 after giving birth to my Grandfather(Patrick) and from
what I can work out a couple called 'Patrick and Mary Donohoe' brought up my Grandfather as there
own child and I think they maybe have been a relation or family friend to the 'Bergin Family' in
someway.

If you can provide any help/info or if I'm on the right track in my research for my ancestors would be
greatly appreciated

Kind Regards

Jim