Sneak behind the first target and take him out. Continue following the straightforward path and sneak behind the enemies as you take them out. Don't worry about shooting your targets as your guns are silenced.
You'll eventually run into two guards patrolling. Mother will tell you to line up and take them out with one shot. Do so and you'll unlock a trophy. (Double Header)
Two heads, one bullet
Continue taking out the guards until you reach a locked door you'll need to breach.
After clearing the room, continue outside and take out the enemy snipers. Take cover and pick them off one by one or if you want to it the easy way, paint the tower using your LTLM and blast them to bits. More enemies will appear so move forth and dig in as you make your way to the bell tower.
Breach the door and move forth. This is a very straightforward path but has lots of hostiles so take cover and pick them off as you continue. Keep heading forward until you finally reach another locked door. Breach it and watch the whole room clear itself. Head to the next building and go upstairs. Follow Mother as he opens the door and head outside to complete the mission.