Having just read Mourning and Melancholia and the very first page of A&T's book proper, I'll make a crude prediction as to how I perceive their thesis will run:

Pankejeff was "two people in one" in the sense that Mourning and Melancholia describes. The melancholia process results in the loved object being reconsituted in the ego. "Attacks" and self-reproaches that characterize depression are really attacks on a lost object which has been absorbed into the narcissistic ego. Hence Pankejeff's sister Anna, who was literally lost due to her suicide, formed a sexually licentious internal counterpart which Pankejeff simultaneously perceived as being himself. He also reproached this internal dual-self for that licentiousness. There's probably something to be said about Freud's economic perspective on melancholia and mania, and the sudden return of these "investments".
If Pankejeff was repressed outside the consulting room, and then loudly proclaimed his libido inside the consulting room, perhaps this ghost-Anna is activated within him, while normally being repressed. Taking as an axiom the truth of the original seduction, this would fit with some of Freud's observations of his homosexual ambivalence.

Update: This is actually a bit of an understatement of what the theory is. The theory is one of 'incorporation' in a schizophrenic way. Note the particular pick-up of the description by RMB (Ruth Mack Brunswick) of the "small brother" and "preschizophrenic sister".

They make the claim that SP's seduction by the sister is the echo of a previous seduction (abuse, in fact) by the father.

First, the sister claimed to repeat with her younger brother a sexual scene that probably took place earlier between her and the father

The father, who later (unable to live with his grief) killed himself. The "incorporated" version of the sister, Tierka, comes to be filled by his wife, and then comes to be filled by his mother. There is a neat symmetry in this account. Perhaps Therese was always aware that she was Tierka, and her suicide finally confirmed this.

When his wife ended her life in 1938, the Wolf Man .... suffered an attack of depressive agitation worse than any he had ever experienced. ... He roamed the streets frenzied and repeated forlornly the stereotypical question: "Why, tell me why, did she do this to me?" This would be the same outcry of despair as that of Father, shattered by the suicide of his preferred object.

It's fascinating how A&T don't trust the literal truth of the analysis but like detectives use clues to draw out a secret truth. They say that Freud focused on the seduction not due to his theories needing support therein, but because his intuition led to his placing importance there.

He was barred from others and -- incapable of assuimilating them -- he could ohnly put them inside himself, as he had some with his sister. His life was made up of maneuverings to avoid hapless meetings and indiscretions. They were all there in him in order to maintain repression of a contradiction: a death-dealing pleasure. This repression appeared only in two images, each incomplete in its manifest state: first the erogenous image of a woman in the position of a scrubwoman, then the second one, a complement to the first, of a phobia-producing erect wolf.