With Jack Harkness, we saw how he was kidnapped by the two women who ran the Cardiff branch in 1899 - Alice Guppy and Emily Holroyd. Emily was the more reasonable of the two, but not by much; she was just as willing to keep killing the immortal Jack until they got what they wanted - either the location of the Doctor and/or Jack's servitude to Torchwood. Alice was the more headstrong member, shooting a young "blowfish" alien to death just to spare herself the tedium of keeping him in custody.
Eventually they died, perhaps in the line of duty, as did their replacements down through the decades. After some time, the souls of Emily Holroyd and Alice Guppy were reincarnated, which is a common enough experience in Toobworld. And as happened with Ross and Demelza Poldark, they were reincarnated so that they would eventually meet up again. (Ross and Demelza came back as Greg Montgomery and Dharma Finkelstein.)
Now with most reincarnated souls, they should have advanced in some way in their next life; stoked up on their karma to make themselves better persons.
Unfortunately, when Emily and Alice were reincarnated, they hewed closely to the way they operated in the past......
(Seen here: Bonnie, Greta, and Charlie Pace in the Looking Glass Hatch underwater from 'Lost.)
Even their personalities seem to match up - Like Emily, Bonnie was more even-handed and probably could have listened to reason had it not been for Greta. Greta was the blonde who was more than willing to keep beating Charlie until the sea cows came home.
Unfortunately, Bonnie and Greta were dispatched by Mikhael. Hopefully before they are reincarnated again, they'll work on the basic nature of their souls to move on to a better level.'