It was mainly an aesthetic choice here. There definitely is a servant hierarchy but it's not so strict. The three of them are basically on the same level with their chunky collars and menial duties.
The two maids act superior to Alison because she is shorter, younger and newer. They're a little taken aback at her ability to "climb the ranks" so quickly, but they take it in stride.
Can it be assumed that the maids were themselves once males (perhaps captured enemy combatants/mercs like Alison's former male identity) who were force-femmed by Valochar or some other demoness, or were they both born atomically female?
