Florence - Peacekeeper
This task is available at pigeon cages.  You need to kill 10 soldiers at the bridge in 60 seconds. It seems that the easiest way to do it is to hire nearby mercenaries.  In fact, this can cause some problems - some warriors goes outside the area and mission is much more difficult.
It is much easier and more effective to do it in another way. You will need 2-3 smoke bombs. Get to the bridge, climb up and kill first group of guards with your blades.  All soldiers will run up to you, but instead of fighting form them into one group. 
Then throw a bomb and change your blades - now with no problem you will kill at least 3-4 of them.  When the opponents will stop choking, throw another smoke bomb and repeat the procedure.  In this way, no one should even hit you. This is an excellent way of completing one of the achievements / trophies (No-Hitter).
Florence - Leader of the Pack
This task is available at pigeon cages.  You have get to the leader of the group, that want to organize a riot. To do this, go to the marked area and target him with your vision. 
Follow the enemy from the roof.  It will be a long trip. At the end you will see the entire garrison gathered in the courtyard. 
Target the commander of the garrison.  From this location you can jump on him and then escape, or just shoot him (if you have a gun). 
Forli - Thin The Ranks
In this task you need to finish three groups of soldiers.  Northern guards are waiting for you on the roof of a low building - double assassination should be ideal here. 
The second group is located on the city walls - get there using line leading to the nearby tower.  Last soldiers are patrolling the street around one of the buildings near the main gate - when they will be close to each other, double murder should not be a problem.