The family tree given here is taken from several sources, some more authoritative than others. The tree can be split into two parts: Moses' and Jessie's ancestors and their descendants. The great majority of their descendants were born, lived and died in New Zealand and we have good records of births, deaths and marriages; they are fairly easy to trace and many of us are, of course, still alive and know our own birthdays and sometimes remember our wedding anniversaries too, as well as those of our parents and children. The register of Births, Deaths and Marriages, managed by the Department of Internal Affairs is an invaluable resource for New Zealand, as are old digitised newspapers collected in PapersPast, managed by the National Library. Similar resources are available for most countries.
Several old family papers trace the three generations of Campbells before Moses (Duncan, Patrick and John, and their families) back to 1729, as well as recording Moses' immediate family. These can be regarded as authoritative, though there are no good dates for births, deaths and most marriages.
For our more remote Campbell ancestors G. Harvey Johnston’s The Heraldry of the Campbells is generally authoritative, though he generally only traces male lines. Luckily he traces our line as far as Duncan, and recorded (in 1920) that he is “now represented by Ewan Campbell of Warritoa, New Zealand.” Much of his information is taken from Burke’s Peerage, another invaluable resource.*
There are many other people who are also interested in their own family histories, many of which cross over with ours. Family trees are available on MyHeritage, Geni and Ancestry.com, though I have found that some are more reliable than others. Most of our current knowledge of Jessie's Cameron ancestors comes from sources like these.
*As Oscar Wilde wrote in A Woman of No Importance: “You should study the Peerage, Gerald. It is the one book a young man about town should know thoroughly, and it is the best thing in fiction the English have ever done!”