Not sure if the Morrisons of Greencastle are connected to yours in Moville but there were quite a few Morrisons in Greencastle:
James and Marianne Morrison, who had two sons William Hugh (died 1875) and James (died 1876) both in infancy and a daughter Charlotte Ellen who died in 1884. Also Marianne Morrison died 1903 and James Morrison died 1951.
William and Sarah Morrison (died 1897 and 1921 respectively). William’s brother Robert died in 1923.
There was a James and Margaret Morrison (died 1965 and 1966 respectively), who lived in Greencastle and their sons were:
James Morrison died 27th February 1983 Greencastle
William Morrison died 18th May 1991
Robert Morrison died 20th July 1993
Their daughters were Margaret Ada died 1946 and Marion died 1976
Also John and Elizabeth Jane Morrison of Carrichue have a memorial in Greencastle.
In Moville there is a John (Jack) Morrison buried, who died in 2004.