Considering that the stepfather and stepdaughter are almost the same age, I don't see anything shameful or surprising about that. Sooner or later, when the wife should have left, the stepdaughter herself would have insisted on this action. Which is actually evident in the course of the video. The stepdaughter immediately exposed her breasts without thinking. Liked her intimate hairstyle - in times of fashion for naked pubes, such exhibits cause additional desire!
The guy is lucky with his sister - she is a nipple. She's ready to open her mouth for him to stick it in her. Apparently she serves him regularly, because he no longer feels affection for her, but fucks her like a street whore - rough and bold. However, she seems to like this treatment.