I think that they were visiting Relugas a fair assumption, maybe for the Salmon fishing on the Findhorn. The season is from mid February to end September which ties in with the date of Tom’s death in early September. Another reason to visit may have been grouse shooting on Dava, again the dates of the season tie in.
I’ve attached an extract from the Death Certificate with cause of death shown as Hemoptysis (or is it Haemoptysis?) and congestion of lungs. Details readily found on the internet, seems a horrible way to die, poor chap.
A more pleasant thought- there is a website from and about the island of Rotuma with email addresses, maybe make contact to see if there are any descendants?
https://www.rotuma.net/