Hi Minnie,
I hope I am understanding correctly regarding Thomas & Charlotte.[Jarvis]
They married in Cork, but you have no evidence that they came here to Australia, only that their son Samuel did. Right ?
Now....
Samuel was born in Ireland in 1819 and came to Australia in 1837.
Samuel married Jane Sullivan daughter of Jeremiah Sullivan[

convict??]
Samuel married Margaret Buckley.
Samuel died 1894 Samuel and Jane had Thomas E. and Patrick
Samuel and Margaret had Samuel J.
There is a newspaper item from The Sydney Gazette in March 1830.
http://ndpbeta.nla.gov.au/ndp/del/homeIt says in effect..
The undermmentioned Prisoners have absconded.......etc.
Any person harbouring or employing them... etc.
One of the names listed is
CUSSEN, Thomas. Morley [ship of arrival] Labouer, Dublin five feet five and a quarter, light brown eyes, dark bown hair ruddy complexion. From No. 8 Iron Gang.
Now, it is a long shot, but could he be your Thomas?
We have found nothing of Charlotte in Aust. so far. Perhaps Thomas came unwillingly and alone.
Another convict was EDWARD CUSSEN. who got his Ticket of Leave in 1842.
http://ndpbeta.nla.gov.au/ndp/del/homealso shows....
A man by the name EDWARD CUSSEN married in Mudgee in 1854. Samuel and Margaret, also married at Mudgee. as did their son THOMAS
Sue