Before we moved to Fresno, we used to visit Hubby's family, staying on the pullout sofa or floor in the living room (read: There were NO doors to that room to close for privacy). We still managed, on a few occasions, to make love VERY quietly, and under blankets so nothing was actually "exposed." Yeah, we knew that someone could've walked in view. But the house was old and had wood floors, so we'd've heard them leaving their own rooms.
Having sex in the room next to your parents is possible. Just be very quiet. Like hunting wabbits.