I composed Ripperologist 128 article with Chris Phillips.
Chris had a great deal of knowledge of the Abrahams family and I hope he does not mind my saying that he was pretty sure too when we wrote the paper.
Jacob Cohen (son of Kasriel) was the brother of Brucha/Betsy Kozminski. It is also highly likely he is the Jacob who committed his cousin Aaron.
When he said "Aaron attacked his sister" as it was written third hand it could have meant Aarons sister or Jacobs sister. I do think it is likely that it was Jacobs sister (Woolfs wife) who was attacked, hence her brothers involvement.
As I said, if it was Matilda (Aarons other sister) I would have thought that her husband Morris would have been involved ?
Wolek Lajb Kozminski ( son of Abram Josif and Golda) married Brucha Kozminski in Klodawa in 1881 And Bruchas father was Kasriel Szlama and mother Ryfka. from Poland, Jewish Records Indexing-Poland, Marriages, 1798-1939
Woolf and Betsy and children moved to Bury New Road, Cheetham, Manchester by 1901 census Cheetham was where Jacob had lived for many years before he went to South Africa. .