Roots Ireland (subscription site) has a record of the baptism of Peter Devery in 1851. Some of the details seem to fit with your Peter but you must bear in mind that birth dates were pretty fluid at the time so there are almost always discrepancies.
The transcription of the record shows the date of baptism to be 21 Aug 1851 but this is incorrect, the actual date is 21 Sep 1851. Pretty close to the date you have for Peter's birth from his obituary.
The parents are listed as Eugene Devery and Elizabeth Rigney. Eugene and Owen are interchangeable.
You can view the original record on the parish registers for Tisaron and Galen (Ferbane) here.
However the mother's name is incorrect so I am not sure this is the correct person.
I searched a bit more of a record for James or Owen.
This couple called Owen/Eugene Devery and Mary Cloonan had 2 children by those names and also another possibility where the mother was simply recorded as Mary Devery.
James Devery 5 Dec 1849
Eugene Devery 11 Feb 1855
Patrick Devery 30 Dec 1847 (Mother's surname not given)
You can also view these records on the link I gave you above.
It seems to me that the surname was almost certainly Devery.
The site www.irishgenealogy.ie is free to search and has civil registrations of births, marriages and deaths from 1864 onwards.
If you search this site for Devery, the vast majority of results are in Offaly. Devereux is generally considered to be a name from Wexford and Waterford, of course there are always exceptions but there are only a few results for Devereux in Offaly and none for an Owen or Eugene.
Using the irishgenealogy site and the parish records you may be able to separate out the various Owen/Eugene Devery families in the Ferbane area and possibly establish which of these families may be yours.
I searched the newspaper archives for any mention of Owen Devery.
I came across an interesting obituary for a John Devery who died on his 98th birthday having been born in 1857 in Endrim, the son of Mr and Mrs Owen Devery, he was the eldest of 16 children. Of this family many of them emigrated to Australia, there is no mention of emigration to the US so this is unlikely to be your family.
This just goes to show you that there was more than one Owen Devery around the area at the time so it is important to sort out which Owen is which. It is however, likely that all the Devery families were related at some level.