Paulalan on Family Tree Circles

Jost Heinrich (Just Henry) ALT served with the Hesse-Cassel legation in London from 1720 until his death in 1768, by which time he was Minister. He had a sister, Maria, who married a KLEINSCHMIDT.
JH Alt married Jeanetta PRESTON, daughter of Sir John PRESTON of Prestonhall, Fife, by whom he had several sons and daughters. One son was Rev. Just Henry ALT, CoE pastor at Mixbury next to the famous Stowe estate (now school) from whom there are many descendants. There was another son, Maximilian, connected with Fulham and Hammersmith, about whom nothing is known.
My interest is in his son Augustus Theodore Herman (Henry) ALT (1734-1815) who travelled to New Holland in the First Fleet as surveyor-general to Governor Arthur Philiip. There they founded a colony that eventually became Sydney, Australia. Augustus seemingly married a Sophia (surname unknown) while in England and had two daughters, although their descent is not known. In Sydney he lived with convict Ann George for over 25 years by whom he had two children, a daughter who died in her teens, and a son Henry (1798-) who left for China on the ship Northampton in 1815 a few months after Augustus died. What happened to Henry after that is unknown.
Augustus's life and career can be found in the Australian Dictionary of Biography (ADB) online. I have also written about him and his family over the years and have posted some queries elsewhere in the past several years which a search will pull up.
Is there anyone out there who can assist with any other info about this ALT line -- births, deaths, marriages, education, places, descendants???
Credit will of course be given for any leads.
Paul-Alan Johnson