Twins.

Your twins have twins! Two double-dicked beauties jousting for a second time for a spot inside you. You feel their first dicks pull you wider as they take a step away from each other. You feel a strange pop and your tailbone dislocates up several inches. In the front, your hard cock is pushed upwards on your abdomen until you feel your stretched-out rubberband simply accept the new guests without any discomfort. They stop pulling on you and your hole once again forms a tight seal around them. Rather than their dicks bunching up together, they remain in a row since your previously round hole has been stretched into a slit.