The FHS site
https://familysearch.org has some basic info for other births/christenings for the same name parents. It appears there were fraternal twins but one may not have survived as the name Mary is reused again later
Francis Reilly Birth May 7 1864 ( 0064) Ballinamore
Father John Reilly Mother Anne Maguire
Mary Rielly Birth May 7 1864 ( 0064) Ballinamore
father John Rielly mother Anne Maguire
Catherine Reilly Birth April 1 1865 (0406) Virginia,Cavan,Ire
father John Rielly mother Anne Maguire
Mary Rielly Birth March 24 1866 ( 0051) Ballinamore, Leitrim, Ire
father John Rielly mother Anne Maguire
Thomas Reilly Christened ( 50) Ballinamore, Leitrim, Ire
Birth April 4, 1868 Ballinamore Father John Reilly Mother Anne Maguire
Mary Anne Reilly Christened (41) Ballinamore, Leitrim, Ire
Birth June 19, 1870 Ballinamore Father John Reilly Mother Anne Maguire
John Reilly Christened (44) Ballinamore, Leitrim, Ire
Birth June 22, 1872 Ballinamore Father John Reilly Mother Anne Maguire
Kate Reilly Birth December 11, 1874 Ireland
Father John Reilly Mother Anne Maguire
Margaret Reilly Birth Feb 24 1877 Leitrim, Ireland
Father John Reilly
Father's Birthplace Drumdarten ??Mother Anne Reilly Maguire
Michael Reilly Birth August 13 1879 Leitrim, Ireland
Father John Reilly Mother Anne Mcguire