Could you type up the details of issue, living and deceased from Mary's death certificate as you now seem convinced that Patrick Daniel SMITH is the son of Michael and Mary. How many children were noted on Mary's death certificate then....six or seven?
The only Patrick Daniel SMITH who died in Victoria was the son of a Patrick and Mary Ann KAVANAGH and I have traced him on the electoral rolls with those parents.
Who went to Western Australia?
Can you post the portion of the certificate that contains the words you can't read following Edward's name. Does it refer to living or deceased or unknown?
How can I get Death, or marriage certificates when I have no idea when or where they were?
norag
Welcome the difficulties of researching one's family history

We have all been there and it is frustrating and for you made all the more difficult with the surname SMITH. Perhaps you could go to a library which has the Diggers Indexes in their resources and you could trawl the SMITH deaths for your people by attempting to match the ages with the years of birth of the three men....but perhaps they died interstate.
Sorry about all the questions but it is difficult to help you with only snippets of the information you have found.
Someone else may have some ideas....I hope so.

Cheers
Cando