Thanks for your reply. From my information, there was another brother, Manus Gallagher, also. He was mentioned in Margaret's obituary as still living in Donegal when margaret died in Bayonne in 1967. Don't know if that helps any more.
My family are Margaret's husband Daniel Ward, who's brother Godfrey (George) was my great grandfather. The three brothers Godfrey, Daniel and Hugh, went to Bayonne in 1910 and 1911. They are the next door family in the 1901 Census on the Donegal site you refer to.