PJ and Gabe toss the underwear, and it lands inside the fireplace. Moments later it's in front of the fireplace. Then when the trunk is opened, it's back in the fireplace.
At around 13:30 when Teddy is trying to "party" with Mrs. Wentz, she goes over to the stereo embedded into the wall. The edge of that set piece closest to the audience can be seen, revealing the kitchen set.
Gabe says that he is 10, but if he was born in 1998 when the show starts he should be at least 11.