Michael Mulcahy, my great-great-grandfather, was from Pallas Grean, Limerick, Ireland. He immigrated some time before 1892, by which point he was already married to Mary Ann Madigan and had two children. His parents were James Mulcahy and Margaret Ryan, and they remained in Ireland. His siblings - as far as I know - were brothers Patrick, John, and James, and sisters Catherine, Johanna, and Ellen.
This 1911 Irish Census is of the O'Brien family; that is, Ellen's family. Living with William O'Brien, 40, and his wife Ellen O'Brien, 42, are Ellen's family: Margaret Mulcahy, 84; Johanna Mulcahy, 51; and Thomas Mulcahy, 17. I don't know who Thomas is. Probably a nephew or a cousin?
According to these dates, William O'Brien was born in 1871; Ellen Mulcahy O'Brien was born in 1869; Ellen's mother Margaret Ryan Mulcahy was born in 1827; Johanna Mulcahy was born in 1860; "visitor" Thomas Mulcahy was born in 1894.
This is the Mulcahy family gravestone in Kilduff, Pallas Grean, Limerick. It marks the burial of James Mulcahy in 1896 (funny, I'll have to ask Betty and John about that; I've been told that when Papa and his father Michael went to Ireland, it was right after the death of Michael's father - but that was in 1905, a solid 9 years after James Mulcahy died). Also listed on the headstone are Ellen Mulcahy O'Brien, d. 1923, aged 54; William O'Brien, d. 1946, aged 77; Johanna Mulcahy, d. 1932, aged 72; and Margaret Ryan Mulcahy, whose death date isn't listed. The stone also gives the death dates of Margaret O'Brien McMahon (18 April 1988), Ellen and William's daughter, and her husband Michael McMahon (7 May 1999). In the 1911 Census, Margaret isn't listed, and Ellen hasn't given birth to any children. That means that she couldn't have been older than 77 when she died in 1988.