Thank you very much for all that... I think all those Loughlins you found are probably the same family, including James McGowan Laughlin. I haven't seen the name spelt with an "a" but they definitely had a son of that name.
I think that the John Laughlin at Waikumete might be worth pursuing, it never occurred to me to search for that spelling, so thank you for finding that, it sounds promising! That birth year of 1824 corresponds with my guess, I was thinking somewhere around 1827, but that's pretty close. I haven't seen a birth record for him. It is starting to look like John may have left the family.
The children of John and Eliza Jane:
Fanny Sarah (Mckee) b.England 1848 d.1920
Isabella (Graham) b.England 1851 d.1926
Agnes (McCormick) b. 1855 Co. Down d.1905 Thames
Samuel Jamieson b. 1857 England d.1931 Paeroa
David John b.1859 Comber d.1919 Thames
Eliza Jane (Whitley) b.1861 Belfast d.1933 Thames
Mary Jane (Wood) no details
James McGowan b.1865? Thames d.1948 Thames
My apologies, some of the details may be incorrect, but you get some idea of the family names to look out for.
The Eliza Jane who is buried at Tararu, from what I can tell, both Elizas are buried there, mother and daughter.