Taking a lead from Ellen Cullen being a witness for Michael Cullen jr’s wedding in 1882, I found Ellen’s birth in 1857 (on
www.irishgenealogy.ie):
Area - Dublin (RC) , Parish - St. Andrew
Baptism of Ellen Cullen 7 Verscoil Place on n/r n/r 1859
Date of birth n/r n/r 1859
Father Michael Cullen
Mother Margret
Sponsor 1 Phelix Doyle
Sponsor 2 Anne Fay
Then i found another sibling of Michael jr at Verschoyle Place, this time showing Michael jr’s mother’s name as Margaret Seymour :
Area - Dublin (RC) , Parish - St. Andrew
Baptism of John Joseph Cullen 12 Verschoyle Place on n/r n/r 1869
Father Michael Cullen
Mother Margaret Seymour
Sponsor 1 Peter Byrne
Sponsor 2 Margaret O'Brien
(This john joseph may have been known as joseph, or else an older probable sibling called john, born in 1861 to michael cullen and “margt seavers” may have died young. Despite the mistranscription of seymour, this should be the same couple as the address is given as 7 verschoyle place.)
Next i got the wedding for michael cullen snr and margaret seymour in 1850:
Area - Dublin (RC) , Parish - St. Andrew
Marriage of Michael Cullen and Margaret Seymour on 23 September 1850
Name Michael Cullen Margaret Seymour
Address n/r n/r
Occupation n/r n/r
Father Cullen Seymour
Mother n/r n/r
Witness 1 Francis Flanagan
Witness 2 Anne Darcy
If you search in St Andrew RC parish for "Michael Cullen" and each of "Margaret", "Margret" and "Margt" in turn, you’ll get a number of their children’s births, including Michael jr in 1856.