I found B rcds for all of the named Whelan children in Mountmellick RC parish with the dates you cited.
For John Whelan M 1831 +/- 4 yrs, Co. Laois, Mountmellick RC parish, I found 2 rcds: 1830 and 1834. The later rcd is more likely the correct one.
For Ann(e) Farmer M ditto, I found 1 rcd, 1834. This and the rcd for John are highly likely to be for these ancestors. A view of the detailed rcds MAY reveal their parents' names as well as other info.
There are NO earlier B rcds for either John or Anne.