Felicity, thank you for responding.I'd forgotten about posting this message and your reply came as a nice surprise.
I've been doing a bit of research into the family over the intervening years and have discovered a little, but of course there is a lot more to find.
I've found quite a few of Sarah Jane O'Brien and John Byrnes' children, however most of them were registered under the O'Brien name. Apart from the ones I knew about from childhood there were a couple I hadn't heard of before (or since).
How do you fit into the O'Brien tree?
Please feel free to contact me by email, and we can chat about common family!!!