OK....going sideways again......and posting the BISA information for Robert Underdown's brother Thomas......
UNDERDOWN Thomas
Parents = Thos and Ann nee HARDING
Baptised 1st July 1821 Southleigh Devon England
died 26th November 1876 Portland Estate SA
buried Alberton SA
arrived in 1849 on the DERWENT*
occupation = Mariner, Labourer, Miner,
Carter, Farmer
Resided at Pt Adelaide, Hindmarsh, Portland Estate
Religion = C of E
Married 30th Aug 1851 Adelaide SA Rachel nee HARPUR
born c1831 WIC Ireland
died 17th Dec 1904 Portland Estate SA
arrived in 1850 on the SULTAN
Children =
Jane (1854-1854),
Thomas(1855-1923),
Rebecca Jane JOHN (1857-1927),
William (1858-1860),
William John (1860-1861),
Anne Elizabeth MATTHEWS (1862-1938),
William George (1863-1916),
Robert John (1867-1917),
Arabella (1869-1870),
Mary Eleanor IRVINE(1 872-1936)
Don't know if this will help us but you never know.....

......dee