"Mommy's Girl' goes the way of a new porn fetish, that I first noticed in many a Brazzers vignette. It's a rear-end fixation of what might be termed Getting Stuck: a girl gets caught in a window, or clothes dryer or couch with upper torso or arm stuck, and the good samaritan takes advantage of the shapely bum sticking out for uninvited sex. This being porn, none dare call it rape.
In this case the mom/stepdaughter team of Rachael Cavalli and Athena Faris both get caught in their couch searching for mom's missing wedding ring. Mom phones the neighbors, Jamie Michelle and her stepkid Kylie Rocket, who arrive, assess the sitution and hump them. A foursome on the couch results to everybody's enjoyment.
In Brazzers world it's generally a one-on-one shtick, so here we get double. Instead of slapstick, this is played straight, though of course the fetish situation (of taking advantage) is more like a stag movie than romance.