Hi Karen and Lu,
He probably had Lachlan as a third name because that side of the family (where the Myles name originally came from) being Christy McInnes's side can usually be "found" by the name Lachlan.
I have just, after many years of searching, found Margaret Eliza McInnes in the US. She married Edwin Levi Crowell and vanished from Victoria in about 1867 with her family. Her son Myles born in 1858 became Godfrey Myles. There was no sign of the name Godfrey until he got to the US but there he is on the 1870 census listed as Godfrey Myles Crowell.
Lachlan Campbell McInnes and his sister Margaret Eliza McInnes came with John (who we are looking for) and his parents (Murdoch McInnes and Christy McInnes) on the Marco Polo. They were first cousins of John. Another uncle and aunt and family being Donald McInnes brother of Christy McInnes were also on the Marco Polo.
Myles father of LCM and Margaret Eliza had re-married and the two eldest children of his first marriage emigrated with family members. The two younger sons that stayed on Skye were Godfrey who came to Sth Aus later and died there in 1912 and John Miles McInnes who ended up in Cornwall.
LCM fell down the railway cutting at Nth Melbourne in 1876 and was killed.

They did a public subscription, via newspaper, for the widow (Margaret) and his young family.
When one of the children died or married the father's name was given as Godfrey not LCM. Lee and I think that the uncle Godfrey came from Sth Aus to help out when his bother was killed. (Godfrey never married.) The eldest son Alexander of LCM and the money they got from the public kept the family together in this case. (This is Lee's line.)
To add to the confusion Sarah Ann McInnes dau. of Murdoch and Christy born 1855 Melbourne married Lachlan Campbell and they lived at Romsey at Glenbride Park. They were very, very well off (had servants). Murdoch and Christy lived in Melbourne city for the entire time and were very well off.
Meg.