Did you find out anymore about your McMaster ancestors in Sligo? I know of 2 McMasters that married into the Frazer family. One I talked to in 1999 when I went to Ballindoon, Sligo. The other was Margaret McMaster. She was married in 1866 and was from Cullnagleragh in the Union of Kilmactranny. Her father was James McMaster and I believe her mother was named Fanny. At least there was a Fanny at the birth of her first son.
It appears from the Family Search records that a James and Fanny McMaster gave birth to a Hubert and he was christened at Riverstown Roman Catholic in 1848. I need to check into this more as I haven't found any other Roman Catholics in my background and it seems like the Protestants usually married protestants. However the name Hubert does carry down so this is possible.