The Slaughterhouse Siblings is a City of London Templar hunt against Charlie and Big Pete, a sister and brother from an old Templar family who punish the Order's debtors. The challenge is to make Charlie kill her own brother.
The siblings are hired to deal with people in debt to the Templars, and they leave victims gutted with their organs swapped for those of exotic animals. In the pub, Big Pete worries about losing his zoo job if anyone finds out he has been letting the pair in, which hints at where their supply comes from.
Charlie and Big Pete work in Bloody Nora's City of London. The other Templar hunts there are Thomas Blackroot and Eveline Dipper, the bounties are Harvey Hughes, Maude Foster and David O'Donnell, and the Blighter strongholds are Field Lane, Black Swan Yard and Rosemary Lane.
The condition is that Charlie kills her own brother, so neither twin can die by your hand first. The challenge wording points to turning her against him rather than fighting both; once Big Pete is dead at her hand, finish Charlie however you like. Listening to their pub talk first gives you time to get into position without alerting them.
They toast Charlie's work that day, agree to keep a low profile for a month and worry about losing their supply. Big Pete's fear of being sacked from the zoo for letting them in explains where the exotic animal parts come from.
Eveline Dipper
Eveline Dipper is a City of London Templar hunt against a black-market dealer who charms people out of their belongings and resells them at a profit. Stealth kill her using a smoke bomb for full sync.
Thomas Blackroot
Thomas Blackroot is a City of London Templar hunt against a gardener whose prize roses around Temple Church grow in soil fed with his victims' blood. Kill him and drop his body in a nearby grave for full sync.
Argus and Rose Bartlett
Argus and Rose Bartlett is a Templar hunt in The Strand against the owners of the Bed and Bottle, a pub and lodging house linked to several missing-person cases. Perform a cover kill on one of them for full sync.
Beatrice Gribble
Beatrice Gribble is a Westminster Templar hunt against a would-be lady-in-waiting who, after repeated rejections, has told the Templars she plans to kill the Queen's consort. Kill her with a voltaic bomb for full sync.