I have a looked at a few Thom's directories around the time of the birth of John F. jnr and later (1848, 50 & 52), but see no listing for a Solicitor or Barrister named John Kearney.. the only Kearney I was able to find in those occupations around that was :
1850 - Anthony R. Kearney, solicitor, 56 Upr Mount Street
I also checked a few later directories in case John snr qualified after John jnr's birth but no sign in 1863, 1872 or 1879
again, just one Kearney listing in solicitors
1863 - Francis Kearney, 31 Gt. Charles St & Limerick (solicitor/attorney/proctor index)
Francis Kearney also listed in 1872 and 1879
You can search many Dublin parish records on :
www.irishgenealogy.ie Note this website concentrates on City records.
Do you know the Kearney family religion ?
Shane