Could this be The Stepford Wives (2004) remake?
The next day, Joanna, Bobbie and Roger go to Sarah's home to check up on her, where upon entering, they hear her upstairs, ecstatically screaming during sex with her husband Herb. As they scramble to sneak out, they find a remote control labeled SARAH, discovering a button that causes Sarah's breasts to enlarge and makes her walk backwards robotically.
...
At the ball, the wives corner their husbands and reveal that Joanna never received the microchip implant. Mike threatens Walter, but Joanna decapitates him with a candlestick, exposing him as a robot. Mike's wife Claire explains that she created Stepford because she, too, was a bitter career-minded woman. When she discovered Mike's affair with her research assistant, she murdered them in a jealous rage. Claire then electrocutes herself by kissing Mike's severed robotic head.
The staircase scene is here (warning, NSFW audio content)
And the scene with the removal of the robot head is here
