Hi
Catherine Bourke baptised on Feb 1830 has William O'Brien listed as a sponsor.
Thanks
It is hard to know what kind of relation the sponsors are unless they had a kind of unusual name !
He could be a relation of some kind , he could also be a neighbour it would have been common enough at the time
He is most likely from murroe.
O'Brien Ryan and Burke where the 3 most common names in Murroe during the 1600-1800's so it would be hard to Pinpoint William O'Brien, there are over 25 William O'Brien in my family tree alone down through the years
One way you could figure it out is using the land records and see if there are Bourke and O'Brien neighbours.