Ewwwww! (Also, nicely done!) It took me a little while to work out what was going on - I’m not as across the Grimdark lore so I was a bit confused that the Sisters were the “baddies” - that’s more on me than the writing though.
The only piece of feedback I can think of (and its very nitpicky) is that the “pacing” of the writing was pretty consistent throughout. A particular example is that the sentences were about the same length throughout the story. I wonder if the use of a few more “punchy”, shorter sentences in the second half might make the action more intense?