A sister saves her brothers, a love is found, lost, and found again, and you put an “o” in front of everything to be polite.
The children's mother 
had died of plague.
La madre de los niños murió 
por una enfermedad contagiosa.
La madre de sus hijos había muerto 
a causa de una enfermedad contagiosa.
A mãe das crianças morreu
 por causa de uma praga.