If you contact the Heritage Officer - Marie Mannion@galwaycoco.ie - she will be in a positon to give you the location of the various cemeteries in the area of Letterfrack. Many burials plots do not have grave markers and as the families die out, the location is not always certain.
Doneen and Moyard would appear to be the main cemeteries in the area. I suggest that you make contact with persons in the Letterfrack area who would have known of the family.
I replied to your IrelandXO of the 21st June 2019 in relation to John Lydon Family in relation to a graveyard adjoining the townland of Baunog.