Death certificate for Patrick or Julia would be useful in finding a year of arrival.
NZ BDM has death of Julia Henigan, 39yrs, 1881.
Is that your Julia?.
Death certificate NZ from 1876 -
Occupation, parental details, where born, when and where buried, marriage details, ages of children of deceased, length of time in NZ recorded on death registrations.
Those details would be much closer in time to the arrival of this family in NZ than are details recorded on certificates for daughters Julia and Catherine years later, so likely to be more reliable.
