Tom:
The baptismal records for the RC parish of Boyle go back to 1793 with some gaps early but starting 1814 records are available continuously. As McCoy points out there are no Martin McGreevey baptismal records in Co. Roscommon and there are no McGreevey baptismal records in Boyle with a father Richard.
Based on the absence of records in Boyle, there is a good possibility that the family attended a nearby parish which does not have records back to the 1830s. The parish just to the east of Boyle is Ardcarn/Cootehall and the baptismal records for that parish start in 1843. I searched for baptismal records in Ardcarn and there are two possibilities.
John McGreevy baptized May 7 1843 father Richard McGreevy mother Catherine Toughran Here is a link to the actual parish register entry
https://registers.nli.ie/registers/vtls000633862#page/7/mode/1up
Roots Ireland also had a June 3 1846 baptismal record for an Eleanor McGreevy with father Richard McGreevy mother Catherine McGreevy. Note: I could not find this record on the parish register.
There are a few other records of interest. The Tithe listings for 1834 for the civil parish of Ardcarn show a Richard McGreevy living in Drumsillagh townland leasing 11 acres of land http://titheapplotmentbooks.nationalarchives.ie/reels/tab//004587398/00…
Roots Ireland also had a February 2 1824 marriage for a Richard McGreevy to a Catherine Taghran Note mother's maiden name for John McGreevy. The parish was Croghan/Killucan just to the south of Ardcarn/Cootehall parish. Marriages were held in the bride's parish.
In conclusion, there is evidence that Richard and Catherine married in Croghan in 1824. They had a number of children and lived in Drumsillagh townland in Ardcarn civil parish and baptismal records are available for the two youngest children. I note that the will did not show John and Eleanor as siblings.
Let me know what questions you have.
Roger McDonnell