Came upon your query by chance in a google search - Don't know if you're still looking for the Dunlavys after all this time.
Edward, Christopher, Sarah and Ellen Dunlavy emigrated to the US on board the SS Spain arriving around 16 April 1883.
Sarah returned to England shortly afterwards because she fell in love with a ship's steward Frederick Johnson Helling. They married in 1884 and had 15 children many of whom died in infancy.
Sarah and Frederick were my great grandparents.
I'm told by a cousin who has previously researched the tree that Anthony Dunlavy's father was also Anthony(1807-1867) and his mother Catherine. Margaret Quinlan's were Edward (1807-1878) and Mary (-1866), although I have yet to find any proof in records - her information is very reliable.
Many records in Ireland were destroyed in an anti-British move,so I'm not sure if we can get back much further. Church records are the only hope and most of these can only be currently viewed by visiting the church or a family history centre in Ireland.
My dad says that he remembers a place in Ireland mentioned was Tubbercurry, which is a town in County Sligo. This would fit in with information from my cousin that the Quinlans came from Sligo. He also says that family legend says that one Irish part of the family was descended from Spaniards shipwrecked in Ireland while heading to the "New World".