Looking for Peter Paniotti Motties

I am looking for the ancestors of my children's great grandfather who's family oral history gives his name as Peter Paniotti Motties who came from the island of 'Sirigor' in Greece. He arrived in Sydney, NSW, Australia in the early 1900's with an uncle, changed his name to Morton, and then moved to Brisbane, Qld, where he lived much of the remainder of his life. The birth certificate of his son born in Brisbane in 1916 however states that Peter was born in Athens about 1892.

I have now learned that Peter Paniotti is an anglicised form of Petros Panagiotos, the latter being his fathers first name and that Sirigor may be a corruption of Tserigo, the common name for the island of Kythera. I am also aware that the name Motties is also probably a corruption of a similar Greek surname. I have searched Australian immigration and naturalisation records for the period and can find no one named Motties entering Australia. I have subsequently searched for similar names such as Mottis, Motis, Motakas etc. I have found one Peter Motis from Greece naturalised in Sydney in 1909 who entered Australia in 1907 after seven years in South Africa. His naturalisation application states that he was born in Athens on 15th January 1881. He is too old to be Peter Motties but may have been his uncle. Are there any descendants of Peter Motis out there or does anyone know anything about the Motties family? Any help or suggestions would be greatly welcomed.