Sequence 5 and 6 have a a total of 6 memories.
This achievement is specific to only sequence 6, but I have included sequence 5 in the list because there is no specific achievement for only sequence 5.
I wrote this guide as a simple checklist (click on the spoiler if you do not mind seeing the title or “subtitle” of the memory) to help you keep up with: what you have completed, how many memories you have left in the sequence, which memories have secondary objectives, and what those objectives are (so you can prepare before starting the next memory).
To keep this solution clean and concise, I have not included hints for the secondary objectives. I wrote this to help in planning ahead (getting enough poison darts, bullets, or smoke bombs) to make the second objectives easier. Please comment if you do need any help and I will provide any help or suggestions I can. I hope you find this helpful and good luck going for 100% sync!