Bonesickle's videos on this (and in general) are excellent. There are two you want to watch for sure...can't remember the exact titles but one is about the trophy...another is devoted to explaining the RPG spawns.
Be warned though, there is still an element of luck because if someone goes down it throws everything off. We had more luck with the third player on the Library balcony near the "number 6 RPG spot" (between the Library front entrance and where the Pak80 is on that small balcony in the corner) than way in the back (Kudos to Mirahh for that). That way, there's a least a chance of helping them (or vice versa) if someone goes down.
Even with a plan, it ain't easy but patience will be rewarded.
Best of luck.
Either way tho, everyone needs to be on same page. Best to go over the plan before starting the game, then once again before entering checkpoint before this part of the level just to make sure everyone gets a quick refresher.
There's a couple different people who have "taught" me the different Adventure levels. For the more difficult trophies, you need to prepare for an extent throughout parts of the whole game leading up to that part. You also need to get this medal (and trophy if you haven't gotten the medal before) your first try. If you waste your hammers and KB's and couldn't get it with them, don't expect to get it without them after you respawn again.
My friend and I played through this particular level enough to where we sometimes get it just helping someone beat the level for their star. It's doable with 2 people, better with 3 tho. It all comes down to understanding of what needs done and who's going to do what. Preparation.
Watch this video:
Everything is explained in detail.
There are three “waves” of RPGs and if I recall correctly, armoured ones only spawn in the last two waves. You need to turn on subtitles so you have a cue when the different scene segments begin and end. Preparation is key and everyone must understand their role - so whoever you get to help you…make sure they watch the videos as well. Even then, you’re probably going to have to try multiple times. Be patient and persevere.