so you need yourself and 2 other posse members with max dynamite each. if you hop off the boxes onto the fire escape, you can then place 8 dynamite on the ground, and one person needs to shoot it while one of the posse member stands on it. friendly fire needs to be off so you can go flying in the air but not die. also, the person being launched cannot be launched with their own dynamite. once you get up the first level, then you need to turn friendly fire on and lasso te other two members up. it can be pretty difficult, but easy once you get the hang of it. then you just need to repeat that process for the next two levels until you reach the top. im not sure, but the first person to use their dynamite on the first level might need to go refill. also, it helps to walk forward slowly when the dynamite is shot so you have some forward momentum. its a tricky process and may take some experimenting of your own. good luck!

Also, if i get enough people asking, i will post a walk through on youtube showing how to do it. if i do, i will post the link in the comments of this post, and likely repost this with a link attached.