On chapter 17 Kei's referenced as her niece. Checking the raws it's indeed 姪, which means Kei is a she.
It was also said they look like sisters (姉妹)
So the translator may not have known that, as they didn't work on that chapter, but the QC and Proofreader did.
Which means the QC and Proofreader are not doing their jobs correctly, because these are things they are meant to catch.
Also on page 14 you have an instance of "Silan", when you probably meant "Silane"
@Snoodlefloo are you the SNOODS who's credited as QC? Can you take a look at this?