I have made the following brief notes when reading the book looking for insights into the author's sources and inspirations:
Grace: "hopeless epileptic"
Dr. Paoli: “Paoli is a Jew, she is a Jewess. They understand each other."
Stefan was an Albanian...
Miss Zillah Lopez
Madame Cadajos Countess Apponiowsky
And Peter knew and had good cause for knowing that umtil now his life had been a failure, not the less complete for the absence of any particular demerit.
When Peter and his mother found themselves surrounded by people, they adopted a mixture of tongues. Changing swiftly and alternately to French, German, Spanish or Italian, they could talk in almost any circle of strangers without being understood.
Peter Blake appears to be an alter ego for Sydney Schiff.
The author's understanding of epilepsy is quite distasteful to a modern reader and shows a complete lack of understanding of the nature of the condition.
There are quite subtle references to Jewishness in the novel. Schiff appears to be writing about psychology in its infancy. Paoli seems to be a Jewish psychiatrist.
The Schiffs had a manservant who was caricatured by Wyndham Lewis in his novel "The Apes of Wrath" under the name of Hassan.
Violet's second name was Zillah. She came from a Jewish family: her father ha changed his surname from Moses.
Schwalbach was the original family name of the Schiff family; it was changed by Sydney's grandfather in about 1810. It may be a complete coincidence that Sydney Schiff chose it.
Sydney Schiff felt his life to be a failure, certainly in the eyes of his own family. This changed after his meeting with and marriage to Violet.
Sydney Schiff's family was cosmopolitan. He himself was proficient in French and German. His father and uncles were fluent in several languages. Sydney Schiff's mother was born in Vienna to English parents. He was devoted to his mother but estranged from her by his marriage to his first wife.