Complex sentence: One such group numbering about forty were gathered under the tutelage of Father John Murphy near the village of The Harrow on the evening of the 26 May, ostensibly to cut turf for him as their local curate which was a custom at the time.
Split into simpler sentences: One such group, numbering about forty, were gathered by Father John Murphy near the village of The Harrow on the evening of the 26 May. Ostensibly the men had come to cut turf for Father Murphy, their local curate, which was a custom at the time.