Luz and Milagro are the twin daughters of Felicia del Pino and Hugo Villaverde. Their parents have a dysfunctional relationship, to say the least. It seems that the girls were witnesses to a lot of the drama that went on between the two, including the burning that disfigured their father severely and kept him out of their lives for nine years. But the girls don't see his absence as a good thing. In fact, they resent their mother for driving away the one person they think can save them from their mother's insanity.
The girls have developed some serious coping mechanisms to protect themselves from Felicia. They use a special language they've developed to demonize their mother and to insulate themselves from her nonsensical actions:
My sister and I call our mother "not-Mamá." As in not-Mamá charred the chicken and is cursing in the kitchen. Not-Mamá is playing that record again, dancing by herself in the dark. Watch out, not-Mamá is feeling sorry for herself. She wants us to tell her we love her. When we don't, she looks right past us as if she could see another pair of girls just behind us, girls who will tell her what she wants to hear. ("Shells," 121)
Though it is easy to see that the girls create this "tight and impervious" double helix to protect themselves from a horrible situation, it is a little hard to feel sympathy for them, especially since their hardened language might be echoing something they've heard their father say.
Unfortunately for the girls, their father is not their knight in shining armor. Even though they are willing to accept that he is maimed and poor, their allowances will never be enough to fix the man who beat their mother into insanity and ruined her health. And as we all know, a leopard doesn't change its spots. When they discover him on top of a prostitute, it's pretty clear that Luz and Milagro will always have to rely on each other to stay safe. Neither Not-Mamá nor Hugo Villaverde are fit for the job.