To receive this Achievement, you must progress through the story until you get your hide out. That's when the Templar Hunts open up.
I got this Achievement by doing Templar Hunt #4 in Nassau (633,784)
The first 3 of the 4 mini missions are pretty straight forward:
Mission #1 "Oh Brother...": During the short cut scene the Mission giver tells you who the target is and the area in which he can be found. When you enter the GREEN area, HIRE the DANCERS FIRST It makes the eavesdropping so much easier, just stay blended with the dancers and follow the two gents as they talk about how funny the word "smuggler" sounds. Use your Eagle Vision to ID your target. When the conversation ends, climb the building on your right, when he's highlighted ... take him out, its best from the roof with an air assassination.
Mission #2 Your asked to follow "discreetly" and act as a body guard. Just stick to the stalking areas. Tag the two with Eagle Vision. The guy your protecting is afraid of being robbed. Use your Eagle Vision every now and again to ID the thieves, They'll be highlighted as enemies (in red) Take out the 2 thieves stealthy or you'll fail and have to start this mission... #2 again. Once you get to an open area, hire the first set of dancers you see and blend to continue following the brothers. When the last thief arrives, take him out while blended with the dancers. After another eavesdropping session has ended, you'll have 60 seconds to get to the next search area. Once there, get to the rooftop, ID the target with your Eagle Vision and take him out (air assassination) when he passed by. After a cut scene you can move to Mission #3.
Mission #3 This one starts off in the Tavern ... BIG FIGHT breaks out. Protect the principal (he's drunk and NOT much help). Oh, did I mention you have NO weapons! Its best to take the aggressors out with Counter Kills or kill chain. No matter how you do it... do it FAST, your new drunk best friend can't take to much of a beating from those thugs! (I'm not sure if you have your smoke bombs or not ... if some one knows for sure, please let me know). After a short walk with your new best friend, hire more dancers and release them right away, their only in the way. MAKE SURE YOU EQUIPT WHAT EVER IT IS YOUR GOING TO USE FOR THE LAST FIGHT... you have all your gear back. While your new best friend is relieving himself, 3 guards come ... and after telling him to "put IT away" they start a fight, Again protect the principal. I used my smoke bombs here (coz I had them) and ended the fight quickly.
Mission #4 This mission is a straight up free run through the trees. Before you start it I would suggest buying the Spanish Officer Pistols (make sure your pistols are loaded) and having Berserk Darts. As I came across guards... from the trees... if there were a group of 3 or more, I would hit the closest one with a dart, watch him kill one of his fellow guards then die... rinse and repeat until all guards are gone. If you need more darts, just craft them on the spot. As you get close to the target area... in this case TARGETS, you will be prompted to use Eagle Vision to find your target. Once located, Air Assassinate him. (This is where the pistol comes in.) After the cut scene your going to either have to shoot or chase Jing Lang. I, personally don't like running, so I shot her. Once Jing Lang has been disposed of, your last task is to escape the area. Another advantage of taking out all the guards on the way in... make leaving a walk in the park, or in this case.. a tree top run.
All in all it took me about 30 minutes to complete this set of missions and I was rewarded with the Help A Brother Out Achievement. Hope this helps.