All Her Beautiful Deaths by Allison Rushby

London, 1865. Desperate for work, Minnie takes employment as a maid for the wealthy Culpepper twins. The siblings lead a strange and unconventional life: Edmund operates a laboratory from the house while Edith experiments with morbid photography. Drawn in by a dangerous attraction to one of the twins, and with a sick sister of her own to provide for, by the time Minnie makes a disturbing discovery it's too late she must stay and unravel the mysteries of Culpepper House before she becomes a victim of one of Edith's photographs herself.