The records for the RC parish of Castlejordan/Ballinabrackey/Ballyboggan start in November 1826. I searched the subscription site Roots Ireland and did not find a record for a Marcella Davis anywhere in Co. Meath in the 1820s. I also do not see a record for an Ellen Davis. Likely she was baptized in Castlejordan before November 1826. Earlier records were likely lost. I also did not find a baptismal record for a Peter Boyd or Peter Boyle.
I did find the November 26 1848 marriage record in Castlejordan. Here is a link to the parish register which shows the record.