The Horace Elisha seems a perfect combination of the classical and Hebraic in Arnoldian terms.
A. S. Byatt in a short essay published in the Guardian pencils in the background of high mindedness , New Thought and Old Money that obtained in the James family.
Verena is based on the woman Byatt calls Cora Tappen who was married for a while to the famous Samuel F. Tappen. Wikipedia has an article on her cora
A much fuller treatment and perceptive analysis of the milieu which bubbled like a cauldron in James’ day is detailed in Hatch wonder girl
(Cora was married 4 times and as Hatch was the first and most famous husband himself a mesmerist, she is generally known in the literature as Cora Hatch. He was also a Dr. like Dr. Tarrent.)
In mediumistic terms both Olive and Basil want to control Verena. Olive is a Chancellor of the Exchequer and Basil a would be the king. When one looks at the Cora Hatch phenomenon Ransome’s views are less antipathetic than we might from a modern day perspective suppose them to be. He sees a beautiful, clever young girl whose talent for impromptu speechifying is to be used in the service of dubious ideology.
The more Olive learnt of her visitor's life the more she wanted to enter into it, the more it took her out of herself. Such strange lives are led in America, she always knew that; but this was queerer than anything she had dreamed of, and the queerest part was that the girl herself didn't appear to think it queer. She had been nursed in darkened rooms, and suckled in the midst of manifestations; she had begun to "attend lectures," as she said, when she was quite an infant, because her mother had no one to leave her with at home. She had sat on the knees of somnambulists, and had been passed from hand to hand by trance-speakers; she was familiar with every kind of "cure," and had grown up among lady-editors of newspapers advocating new religions, and people who disapproved of the marriage-tie. Verena talked of the marriage-tie as she would have talked of the last novel—as if she had heard it as frequently discussed; and at certain times, listening to the answers she made to her questions, Olive Chancellor closed her eyes in the manner of a person waiting till giddiness passed.