I call bullshit. A BJ requires quite a bit of head movement (unless the guy has a two-inch dick). The sister's head would be whipping around like she was on a bucking bronco. That guy is in for a life of hell. Wait until the honeymoon is over and they get into their first argument, it's going to be and epic vocal tag-team match. While one head tears him a new asshole the other will be recalling things he hasn't even done or said yet to add fuel to the fire.