I read your email with interest. I am too interested how the Lumsdens came to Australia and havent found a link either - but - Mitchell appears in the Lumsden Family Tree, which I have extensively built, in this way: Philip Kinnear Lumsden married Annie Cathro Mitchell on 23/3/1888 and I've read the marriage certificate, at Kirremuir. Her parents were Hugh Mitchell and Annie Cathro Mitchell. Helen mitchell is a name which popped up as being a witness to the marriage of Philips Brother, John, born 1871, who married Elizabeth Anderson. Philip and Joan are two of ten children, parents Alexander Lumsden and Mary McKenzie, at Longforgan Perth. I am directly ascended from Alexanders brother, William born 1824, who is my great great grandfather. Did you know there is a Lumsden grave at karakatta cemetary, Perth WA?
It looks like Mitchell may have to be the next research task!