John:
The 1855 Griffiths Valuation head of household listing shows a John Oates in Ardmore townland.
http://www.failteromhat.com/griffiths/roscommon/killukin.htm
Roots Ireland has baptismal records and marriage records going back to 1811 for Killukin parish, However, I was not able to find the children using the name John Oates as the father. There is a Dominic Oates born in 1839 but with a father with a different first name. Roots www.rootsireland.ie is a pay site so I did not call up the record.
Did the Oates family emigrate?
Roger McDonnell