Both of these souls are located in the Lust circle of Hell.
Francesca Da Polenta- is located at the beginning of Lust. You'll find her right after you climb down after defeating the boss in Limbo. Make sure to ABSOLVE her.
Paolo Malatesta- is found during the boss fight in Lust. After the first part of the fight you'll come to a stop on the platform. You will see a purple fountain (mana) with a rope/ladder near the edge. Go down the rope/ladder to find Paolo. Make sure to ABSOLVE him.
Ding, trophy acquired.