Don't know about Sarah then. That might be her maiden name. Might be a sister.
I've gone to the Kent OPC site and clicked on the parish list link and nothing happens.
New South Wales, Australia, Assisted Immigrant Passenger Lists, 1828-1896
Name: Timothy Willis
Birth Year: abt 1812
Arrival Date: 1 Sep 1839
Vessel Name: Cornwall
Brought out by Government
Occ: Farm Laborer
A Native of Tenterden, son of Thomas Willis Laborer and Rebecca his wife
Death 7707/1888 WILLIS TIMOTHY AGE 78 YEARS DIED BOWRAL