Elizabeth Williams

Aunt to the main character, daughter of Allison, sister of Amelia and mother of Catherine.

Has a very close relationship with her daughter, both openly talking to each other about things that happen, including sexual stuff.

It is a recurring motif that she is a "lightweight" drinker, i.e. she gets drunk quickly and often passes out, requiring MC to carry her to bed.

Once she and MC starts having sexual relations she quickly turns out to be nearly insatiable, always flirting and acting in a seductive manner. In addition, she not only is ok with MC also having sex with her daughter, they often share him as well! (For whatever reason, both of them calls MC "daddy" in sexual contexts.)