The heroines of the story are unfulfilled: their strict religious mom is always ragging on them and grounding them. When their youngest sister, Cecilia, escapes the controlling environment by killing herself, the rest of her sisters focus their energies on escaping somehow.
After Cecilia's death the family finds a sort of peace. The parents ease up on the rules and even let the girls go to the homecoming dance. They might have found a way to lead normal lives without resorting to suicide.
Lux misses curfew after the dance and the girls are put on lockdown. Their mother becomes a monster, yanking them out of school and never letting them leave the house.
Lux starts meeting men on the roof of the house for sex. The other girls are wasting away.
Death Wish Stage
The girls bring about their own deaths by suicide. The heroines of our story destroy themselves.