I'll go ahead and tell you now: This trophy is a pain. Just, and only, because of Chapter 2. Be prepared for frustration and arguments abundant. Make sure you have good communication and above all else: Take breaks as needed, but DON'T leave the match. If you do, you lose the checkpoints too.
Would also advise that you use the sub-reddit to find other players, if not this site or your friends. This is the sub-reddit I used to find my group:
https://www.reddit.com/r/GhostOfTsushimaLegend/With that said:
Chapter 1:
Chapter 2:
Chapter 3: