Trigger Error

Because everything is happening on one slide, you don't need to use variables. And you don't need to use separate objects and triggers for the checkmarks.

Slide 1 in the attached file shows what I mean.

• The checkmarks have been pasted directly into the Visited states of the icons/pictures. 

Note: Visited is a built-in state, so no triggers are needed to change an object to that state. The object will change automatically when it is clicked. 

• The triggers to show the parts of your next arrow run when all of the icons are Visited.

Slide 2 shows a quicker change. Instead of changing the next objects to Normal when the checkmarks = Normal, the triggers run when each checkmark is not Hidden. That makes it work. (It can cause issues to run a trigger when an object's state = Normal, because each state has a bit of Normal.) 

FYI: In both of the edited slides, I deleted the audio and adjusted the position of the icons on the timeline, so they appear much sooner. That was just done so I wouldn't have to wait for the audio when testing the triggers. 

By the way, there are times when variables are helpful for controlling a button. This post has more info: TIP: Controlling the NEXT Button 101 - Articulate Storyline Discussions - E-Learning Heroes