I am not related to your tree, but I have a distant relative who went to the Falklands, so I tried looking for some ship's voyages made by Donald Stuart McPhee. (I looked at your public tree to see what you had first).
...Regarding the 1935 voyage to Southampton, the name of the ship was ARLANZA, he was aged 57, and he was heading for: The Laigh, Huntingtower, Perth.
Now, there are earlier journeys by a Donald McPhee on the OROPESA from Liverpool to Port Stanley in 1909; on the ORAVIA from Liverpool to Port Stanley in 1910; and from Liverpool to Port Stanley on ORITA in 1917 ... but he is a shepherd at this time. Is this the same man?
Also, there is a Donald McPhee aged 31; Alexander aged 25; and Angus aged 20 ... all on ORAVIA leaving Liverpool on 17 Oct 1912. They all seem to be farm hands.
Are they part of your McPhee forebears? Is any of this new to you ... I doubt if it is!
P.S. I know from your tree that Donald died in Australia, so I tried to find a voyage for him anytime after 1935, but to my surprise it didn't come up.
P.P.S. The name of my distant relative in the Falklands was Greenshields. He was a farmer and after a while, he moved on the South America. He and a friend whose second name was Douglas were apparently responsible for setting up the the place called DOUGLAS STATION on the Falklands. One of the Greenshields drowned while out there, and must be buried somewhere there.