Just a quick update in case any other researchers stumble upon this.
I found that David's brother Isaac Lees sailed from Auckland to California in 1898 and I have found further records of him in the state of Montana where he died in 1919. The informant of his death certificate was a James Leeds (sic) who may have been a relative. Curiously, though Isaac's parents' names are correctly listed as William Lees and Miss Moore, there is a ? next to the married field. I also could not find Isaac on the 1900 or 1910 US censuses. The man still remains a bit of a mystery.