I dont see an O'Hara Cottages listed separately - but here is an O'Hara Buildings in the 1880s and 90s, right beside the barracks and at Harolds Cross Bridge junction. The buildings are not labelled on this, but see the area on the c1890s OSI map
Grand Canal Bank, Harolds Cross (press 8 , or click on the 25" historic option to see the correct map)
When the map page starts up , the red cross in centre of map marks the poss. location of the buildings
The barracks are just to the south east of this location.
In 1894 the Thom's listing is :
O'Hara's Buildings
Harolds Cross Bridge, Grand Canal Bank
1. Masterson & Co., tea, wine & spirit merchts, and 1 Terenure Rd.
2. Tenements
3. Mr. James Elliot
4. Mr. William O'Hara
nine small cottages (presumably these were referred to as O'Hara's cottages)
Shane