Barrett, Burke, Costello, McHale, - Co Mayo

Hi, I have a number of brick walls in my Irish side of the family but a good place to start would be my 2xGGF Michael Barrett. According to Scotish census records he was born in Kilmaine somewhere between 1824-1835 (each census has a different birth year estimation). He died in 1889 apparently aged 54.

He married Ann Burke c 1831 Co Mayo. To my knowledge she was baptised 4 Dec 1831 - parents John and Margaret.

Michael's parents were Patrick Barrett c1801 and Mary Costello c1804 and his siblings Rose, Thomas, Patrick, Margaret, John, Walter, Edward, Ellen were all born in Ireland so perhaps in the same parish?

Patrick Barrett's parents were Patrick Barrett and Cecilia McHale. He was born in Kilmore c1801. To my knowledge the parents remained in Ireland.

Mary Costello's parents were Patrick Costello and Bridget Jennings. Mary died in Edinburgh in 1888. 

As a side exercise, I am also trying to find out if my Mary Costello is related to a Patrick William Costello 1824-1896 who emigrated to Australia in 1847 along with his sister Mary. They were born in Leitrim. Their mother was Jane Maxwell. Father first name unknown.

I realise that once we get back to prior to the potato famine records are scarce but if anyone is able to find any church records or give me any pointers for finding more information I would be eternally grateful.

Thank you, Cathy