Slevin/Slavin Ancestors

I am also looking for ancestors who came from Donnegal and really need some help/advice. My gg-grandparents Bartholomew Kelly and Margaret McDevitt I believe were married somewhere in Donnegal which I know is like looking for a needle in a haystack. They arrived in Quebec Canada sometime between 1830 and 1835. Their first child was born in Quebec in 1835 and is my g-grandfather Charles Kelly. I believe that Bartholomew may have had a brother named James who either immigrated with him or prior to his arrival as James turns up in the same parish as Batholomew and is godfather to Bartholomew and Margaret's 1st child Charles.

Bartholomew died in Montreal in 1895 aged 83 which would put his birth around 1812 or so. His wife Margaret died at a young age in 1852. I have registrations of the births and deaths of their children, have actually seen the church registers and been to the graveyard and walked on the land that they had farmed. I really am looking for any information as to when they might have married in Ireland, when they might have immigrated(I have had absolutely no luck with immigration lists etc.) and if possible birth registrations. I know this is all a very long shot but thought I would take the change of writing anyway. Will be very glad for any help whatsoever.

Margaret