What is your source for his year and place of birth?
As John is/was the commonest boy's name, Joseph was almost the standard middle for boys between 1880 - 1950, and Kelly is the second most common surname in Ireland, it is essential to have further information to pursue this matter.
Regarding Rathangan research:
BMD Registration: it is in the Union and Superintendent Registrar's District of Edenderry,
it is in the RC parish of Kildare and Rathangan.
Griffith Valuation: it is in the county of Kildare, barony of East Offaly, but some of it's hinterland is in the barony of West Offaly.