Petros/Petrus/Peter Emmanuel Kassimates

Hello all,

I am trying to establish the family of Petrus/Petros/Peter Emanuel/Emmanuel Kassimates (His preferred spelling was Petrus Emanuel Kassimates). He came to Australia in 1911 (according to his National Archives naturalisation application) and was born in 1888 in Alexandrades, Kythera. In 1928, he married Grace (Chrysanthe) Panaretto, the daughter of Anastasios and Martha Panaretto/Panaretos. Petrus and Grace had two sons, both of whom married but did not have children. Both sons are deceased. Petrus worked as a confectioner and had a cafe at one point. After living in Sydney and Melbourne, the family settled in Elmore, Victoria.

I am having trouble establishing who Petrus' parents and siblings were. His National Archives documents and marriage and death certificates give his father's name as Emanuel Kassimates, and it seems that is a very common name in Kythera.
His mother is listed as Stamatiki Kassimates, maiden name unknown. Not knowing her maiden name is making it difficult!

I have searched everywhere online, taking spelling differences of the surname into consideration (variations with the C and K, with two Ss and one S, ending in -es,-is,-i and -y), but haven't been able to establish any siblings or parents, or even get any clues.

I did consider a family who moved to Queensland, with parents' names Emmanuel Kasimatis and Stamatiki Paspala, but it doesn't seem to be the correct family.

Can anybody assist or provide any information?