The actual optional objectives are pretty straightforward and will be pretty clearly given to you, so if you set things up right this isn't hard. However, there are two game wide quests that could block you from getting this.
First, when you do "In God's Hands" you must heal everyone. Otherwise Brother Nicodemus may not be willing to come with you.
Second, do not complete the "Gallow Brothers" quest until you have this trophy. Andrew must be alive to get the trophy.