Welcome to Ireland Reaching Out!
All of the surnames you mention are Co. Donegal surnames. Researching in Co. Donegal is very difficult because almost all parishes do not have records until 1850 or later. For example, you posted in Kilmacrenan parish and their records do not start until 1862. I did search on the subscription site Roots Ireland but did not find any records for Hug Dugan, Leitita Gallagher or Cecelia Dugan.
I would consider posting Hugh's emigration story on our XO Chronicles site and possibly someone will see a connection.https://www.irelandxo.com/ireland-xo/history-and-genealogy/ancestor-data...
I would also consider DNA testing. You may get matches with other with Donegal connections and can get more info on the origins of your family in Donegal.