Hi Heywood, thanks for joining in on this search, I really appreciate everyone's help on this, you are all very kind.
Jomot, very useful to cross reference the baptisms which I had not thought to do. That just left Marguarite Owen as their child and McKean Street is just a few streets from Cecilia Street, where Richard Stanley Owen (Mary Ellen's first son) was living when he married.
Unfortunately I still think I have the wrong marriage cert for Mary Ellen Stanley as I have just found another Mary Ellen Stanley who was born in Ancoats, Manchester which was to location of Robert Owen's first marriage.
Manchester, England, Church of England Births and Baptisms, 1813-1915
Birth, Baptism & Christening
Name: Mary Ellen Stanley
Mother: Sophia Stanley
Father: George Stanley
Baptism: 6 Feb 1876 - Ancoats, St Andrew, Lancashire
Added - although the age does not quite fit?
Heywood - Mary Ellen Stanley was in Barrow-in-Furness in 1891