Having sex with two cousins while their parents are away

My two cousins and I are quite close, but the feelings I have for my cousin are more like love than affection, so I often go to their house to visit when their parents are away, then I accidentally catch their eye. The two of us had sex in front of the younger sister. The younger sister was shy, but because of her older sister's lust, she dragged the younger sister into a love triangle.