Sequence 2 is the best option here. So far. Just got into Sequence 3 but a bit of work in 2 and you're good to go.
For 100% Synchronization you need to complete a certain task within each memory of the Sequence.
*SPOILERS* For better descriptive purposes.
Sequence 2 consists of 8 memories.
Memory 1 – Do not drop below 1 health square.
-Essentially just walk to the left of your starting point, down the stairs and straight for the doctor. Heal up and don't do anything overtly stupid as you climb the church and its yours. You will probably get this without having to read this.
Memory 2 – Kill your target with the hidden blade.
- Make your way up to Carnefice's house and climb up to the roof. Make sure your hidden blade is equipped then hit LT to lock on Carnefice. Walk a bit out onto the beams and assassination option should pop up with X and there you go.
Memory 3 – Throw the Borgia Captain into the scaffold to kill him.
- It does not matter how you get to the Captain but you will notice there is some scaffolding just to the left of the little alcove he is in, the wooden beams all tied together. I killed all the other guards first and then manoeuvred my way closer to the scaffold. You will notice that B has the option of grabbing. Grab the Captain then I think B switches to throw. Tilt left stick in the direction of the scaffold and hit B.
Memory 4 – Don't lose any health.
- Honestly, just be a perfect citizen and this is yours. Again you will probably not need help with this one.
Memory 5 – Catch the Borgia courier in under 1 minute.
- After the fight the Courier is right in front of you. Sprint/freerun after him. He took a left right away for me. Once you're close enough let go of A and B should say tackle and there you go.
Memory 6 – Don't lose any health.
- This one was a pain for me. You have to fight 13 Romulus followers and not get hit. Pretty much as quick as you can pull out your sword and hit RT. Counter the first attack. If you know how to chain the one hit kills only do it for two guys at a time, otherwise another will hit you while you are attacking his buddies. So counter first attack, let go of RT, left stick in desired direction and X then once more for one hit kill then hold RT again. Rinse and repeat. This took me many tries as Ezio didn't want to pull out his sword fast enough. But patience and practice will get you through. And if you waited until after the memory, you can pause and Restart Memory if you get hit. Cuts down on waiting time. Any other tips for this would be greatly appreciated.
Memory 7 – Complete the memory within 8 minutes.
- Best advice is do it once and just make sure you know the route you have to take. A couple tips. When you have to pull the levers at the start. Get up to the platform for the first time go right, jump the gap and pull that one then go back the way you came across that gap and another then pull that one and work your way around the room counterclockwise. I accidentally jumped into the pool of fire and died, and in the last room when the top of the column falls off so you can get back up, a few jumps after that I missed the jump completely and just got back up and opened the treasure and scrambled up the ladder and still got it. So you can screw up one sort of major/minor jump. But as I said, the first time you do it, don't rush and just memorize the path you have to talk.
Memory 8 – You get this 100% pretty much no matter what. I have no idea how you cannot.
Hope that helps, and have fun.
LordMcclure points out that if you are having trouble with the Wolf Clan in Memory 6, switch to hidden blade as it is much quicker compared to the sword.
HadesDC212 suggests using the stiletto for the Wolf Clan
Tom1013 says for memory 7 that skipping cutscenes may help with completing it in under 8 minutes. I haven't verified this but it is worth a shot.
Also you can always go back and play the memory over again as many times as needed. Though you are bound to get this achievement if you are going for the DLC achivement