I do not know if you have already this information.
Susan Trenouth, seamstress 58 of Cornwall
Richard Trenouth, mason 20 of Cornwall
Susan Trewartha/Trewautha (Trenouth ?), servant 33 from Cornwall
The above three people arrived on the Ascendant.
The Ascendant, 562 tons barque, arrived at Port Adelaide, South Australia on the 15th January 1851 with Captain Robert Spencer from London 22nd September 1850 via Plymouth 3rd October 1850.www.theshipslist.com/ships/australia/ascendant1851.htmwww.slsa.sa.gov.au/fh/passengerlists/1851Ascendant.htm
There were also other Trenouth's arriving in Adelaide.
John Trenoweth / Trenouth and Grace nee Thomas arrived on the 6th January 1849 on board the Rajah departed from London 30th August 1848 / Plymouth 9th September 1848.
SA Passenger Lists/ Arrivals in South Australia up to 1849http://members.ozemail.com.au/~leadbeater/passengerlists/
John Trenouth aged 34, Mary Trenouth (n/a), Mary Trenouth aged 9 and Elizabeth Trenouth aged 8 years
arrived at Port Adelaide, South Australia on the 7th October 1852
on board the Sultana (ship no. 52/15), 588 tons, Captain David Mainland, from London / Plymouth 21st June 1852.www.theshipslist.com/ships/australia/SAassistedindex.htm
State Records of South Australia
passenger lists - incomingwww.archives.sa.gov.au/archivesearch/intro.html
I hope this is of some help.
Good luck with your research!