Sister has to come home to take care of sixteen year old brother while mom is away. (I would say that this is somewhere between Much Sex and Some Sex.)
After my son left home his younger sister told me how he had raped her two years before. Once that secret was out, she continuted to tell me what he and she had been doing since then.
When he was born his Older Sister took charge of him from their Mother like he was her own personal Barbie Doll. Her love for him lasted throughout their years in school and later in life. They moved in together and she makes love with her Brother with a big surprise.