Some comments that I hope you will find useful. "Llanfendigaid" roughly translates as "Parish of the blessed". It is located on the coast equi-distant from Dolgellau and Machynlleth about 3 miles north of Tywyn. It did once belong to the Anwyl family but John Nanney I married Elizabeth Anwyl and produced John Nanney II who married Blandina Corbett who produced the 3 children referred to below: John Nanney III b 1673, d 1722 in Wales, Vincent Nanney d 1714 and Lewis Nanney. I don't know much about any of them. My family is descended from John Nanney III so although he might have visited the US, he did not stay. But I doubt he did even this - as the eldest son, he had no need to seek pastures new. None of them would have gone to Australia since it had not been discovered by Captain Cook at that date.
The Nanney-Wynn name came about as a result of the marriage of John Nanney III's daughter Lowry Nanney to Robert Wynn. Their son William Wynn inherited the Nanney Estates from his childless uncle John Nanney IV on condition that he used the name Nanney. He therefore changed his name variously to William Wynn-Nanney & William Nanney-Wynn.
Much later in 1823, a Sarah Nanney-Wynn married a David Kirkby and the family became Kirkbys before my Great Grandfather changed the name back to Nanney-Wynn by Deed Poll in around 1925. His eldest cousin was William Wynn Kirkby and he inherited all the Estates which were sold off in the 1920s on his instructions by my Great Grandfather whobought Llanfendigaid from the Estates before sending the money to William in Australia where he had emigrated.
I have no record of any William Nanneys or George Nanneys. George was no a family name so seems unlikely. William would be a possibility though.
The name Nanney comes from a place "Nannau" near Dolgellau. The estates existed largely between Barmouth (Abermawr) and Talylyn near Tywyn.