Thanks for quick response. Sorry, I'm not very near Sydney [about as far you can get!]. Born in Cardiff - that's "old South Wales" - I now live 100 miles from there.
Here is more info on the Welsh background of Leyshon.
IGI has his baptism, St John's Cardiff, 11.2.1783, and his marriage, on 2.4.1832 to Elizabeth Lawrence, in St Bride's Major [village 4 mi. South of Bridgend in the Vale of Glamorgan]. I have found in IGI on-line their 5 children [1831-1837]- probably you have all details. FreeBMD records one Eliz. Davy, 65, died Q1. 1875, Cardiff 11a, 222; this might be his wife/widow.
Leyshon had a sister Mary who marr. 'my' Thomas Vaughan [surgeon, 1778-1819] at Cardiff 16.3.1806 - she is a 'minor' per marr. licence therefore b. after 1785.
Leyshon and Mary are the only children [known to me]of Jonathan Davy and his wife Mary [nee Hopkins] who marr. on 4.7.1780 at Coity [3 mi. N. of Bridgend]. Jonathan appears in Cardiff Records as a Churchwarden of St John's Cardiff for the year 1783. He is noted in a 1795 Cardiff Trade Directory as 'Grocer & Wine-Merchant', but he died, and was buried at St John's on 19.11.1798. It was his widow Mary who signed licence for the young Mary to marry in 1806; she may be the Mary Davy who died [per FreeBMD]in Q2. 1859, Cardiff 11a, 157. I have looked for earlier references to Davy family in the Bridgend family, so far in vain, and wonder where Leyshon got his name from: it's a real Welsh language name, not at all common in the Vale of Glamorgan which was already anglicised at this time.
I hope some of this is useful to your researches.
Best regards - Phil