I think zeroing in on their DOBs and looking for parish records may flush out some immigrant siblings, thus additional papertrail.
Looks like Pat Jr in 1900 Name: Patrick J Cull Age: 31 Birth Date: Sep 1868 Birthplace: Wisconsin Home in 1900: Milwaukee Ward 4, Milwaukee, Wisconsin [Milwaukee] Race: White Gender: Male Relation to Head of House: Roomer Marital Status: Single Father's Birthplace: Ireland Mother's Birthplace: Ireland
Look at this fab fabulous digital collection!
Pat & Hanora's marriage cert Nov 21 1865 witnesses:Jeremiah Cosgrove & Johanna Ryan Celebrant?S.P. L_________ S.J(?)?????????????