Thanks Alison,
Yes, you have the correct marriage. Not sure where they married or the names of the children. I think Walter Blakley Swan was one of them. I have Walter plus 4 sisters as their children, (from website write up on N W Swan!)
Mary Helen O'Brien was from Ireland too, but judging by the dates etc they must have married in Oz.
There are a few marriages between the Greacens and the Swans here in Ireland. I'd love to find where the grave is.