So . . . The following are just possible leads to get you back further with Francis Cullen . . .
Please note that these are just works in progress at the moment . . .
I am looking at Francis' parents possibly being Patrick Cullen and Johanna Connor . . . I know you had mentioned these before . . .
So Patrick and Johanna married in 1838 and had a son called Francis born in 1839 BUT this is too early a birth for your Francis as in 1869 he states that he was 19 giving his birth year to be approximately 1850 . . .
But, it was relatively common for a couple to have a child, this child to pass away, and then to christen a later child with this same name.
Looking at Johanna (or Jane) . . . A Jane Cullen passed away in 1883 in Stepaside . . . Stating widow . . . Son James informant . . .
I would have liked to see Francis naming his first or second daughter Jane (to establish naming patterns) but reviewing I noticed that his first daughter was christened Mary JANE Cullen . . . Not an exact science but a good start.
I found a Catherine Cullen born to Patrick Cullen and Johanna/Jane Connor in 1841 and she's a very good match to the Catherine Cullen that I mentioned earlier that married a Joseph Doyle in 1865.
There is a death for a James Cullen in 1884 in Stepaside who looks to be a good match for the son of Patrick and Jane Cullen . . .
Again, all these are just works in progress for now but I just wanted to type them up before I couldn't decifer my notes 😁
Tara