Hi Linda,
I'm not sure that we have a connection, but will try to put together a time-line for my O'Briens and get back to you.
I started from the fact that members of my family (O'Brien descendants but mostly of the girls, so different married names), all turned up at the various houses 28, 29 and 30 Upper Ormond Quay over a considerable space of time and then spotted that the only constant seemed to be a family of O'Briens living at 27.
If ours are related it would be through the earliest O'Brien that I have info on at present - so no parent or sibling data as yet, but there seems to be a connection to a James, who might be the father.
Do you have a father's name for your William? Or any address where he resided before Upper Ormond Quay?
With such a common name, it's possible that this is all a co-incidence but was hoping that it might lead to another step backwards.
I'm going to be away again in between so it might take a couple of weeks to list out all the addresses (with dates) relating to this family, but I'll try to get back to you soon, with that info.
Sheila