I, too have a family story about 6 brothers immigrating to the US from County Mayo. My gggrandfather, James was born in England in 1850 and his family immigrated to the US in 1852. Two of his siblings, Peter b 1856 and Catherine b 1860 were born in upstate New York. I have not been able to find this family until the 1870 census - where they lived in Northumberland County, Pennsylvania. Here the two brother worked in the coal mines. Contact me if this sounds familiar.