Hi, Erin,
I found quite a bit on Patrick Shaughnessy in the excellent book "The Irish Aboard Titanic", written by Senan Molony, with a great deal of research by Phil Gowan.
28 year old Pat Shaughnessy, from Tynagh, Co Galway, boarded at Queenstown (now Cobh). He had an older brother named Tom, a farmer, who stayed in Ireland. According to this book, 'Pake" (his nickname) was travelling to America to join his sister Bridget - she had married a man named Burke and the two were living on Lexington Avenue in New York at the time. He had another brother named Willie (probably William). In fact, in the 1911 census, Ellen (Pat's mother) is shown as having 8 children (the other names are not listed here).
Hope this is of some help. If it is, you can thank Molony and Gowan, two of the best in the business.
Best regards,
Cook