I've only recently begun researching the Carruthers (my 3rd great grand mother's family).
According to my notes, Julia left for Australia in 1892 with 3 of her adult child (all aged between 18-21). Most of the children married in Australia, so it is entirely possible that not even Julia is buried there. It's possible that Cecilia Julia Carruthers/Richardson, who didn't go to Australia with her mother and siblings because she had already married in England, added a reference to both of her parents on her husbands tombstone when he died in 1910. It may just be Richardson who is actually buried there.
As to the captain, his Masters, First Mate and Only-Mate certificates are available on Ancestry, as well as the application form he submitted for his Mates exams in 1862 (which includes ships served on until that point). If you don't have access, let me know and I can transcribe the list here.