Why do Prieto, Lola, Olga, and Mabel gather with all the letters Blanca ever sent?

Prieto, Lola, Olga, and Mabel gather with all the letters Blanca ever sent. They read them together. Lola wants Prieto and Olga to see what their mother is really like. Prieto and Olga have to realize how their mother manipulated their lives and their feelings. How she tried to poison how they saw family members and how she tried to cause discord and resentment among them.