Hi, I'm not sure if you are still wanting an answer to your question as it is quite old. However I think I can help. Ernest Deuchar Johnson was my grt grandmother's half brother. They had they same father George Berry Johnson, however my 2x grt grandmother died after 6 children and George then married Mary Simpson Deuchar, who was born in 1836 in Kirrimuir, Scotland. They went on to have another 5 children - one of which was Ernest. He was born in 1865 in Lyttelton near Christchurch, New Zealand.
Ernest married an Annie Smellie (spelling varies) in 1895 in Christchurch, New Zealand. They had one daugher Edna Deuchar Johnson, born in 1898 in Christchurch. Sadly Edna died as a teenager while the family were travelling overseas. There were no other children.
My father had told me how he visited Mona Vale as a child when Ernest owned it. Ernest died in 1937 in Christchurch.
I hope this helps.