Show layer after others visited

I would add a T/F variable (AudioActive) and use the value to limit any other actions.  
At base layer, set variable AudioActive = to true at timeline start.
on the base layer audio, set AudioActive = to false when the media completes.

On your layers, add the same... 
At each layer, set variable AudioActive = to true at the layer's timeline start.
on each layer's audio, set AudioActive = to false when the media completes.

Perform any of your other trigger actions with the added condition "IF AudioActive = false".

This is above my level of knowledge in Storyline. Is there not another way? 

Hi Kathleen.  If working with variables is what's tripping you up, there is, unfortunately, no way (that I can see at least) of avoiding them.

That being said, I've attached a file demonstrating how I would go about achieving your desired effect.

You'll wanna start by creating three T/F variables with a default value of False. I've simply gone with "completed_1", "completed_2", and "completed_3" to correspond with the numbered layers you have in place.

Once in place, you'll want to create three triggers that change the state of an off-screen object when all three of these T/F variables read "True".  I use off-screen objects frequently to act as checkpoints. I usually set them to the Hidden state by default and have the trigger change the state of the object to Normal. Also, why 3 triggers? This is to account for the different orders in which the learner could view the numbered layers. 

On each numbered layer, create a trigger that adjusts the corresponding variable to True when the timeline ends (when Media Completes is another viable option).

For each numbered layer, be sure to check the two boxes highlighted below. This will save you a trigger (Hide layer when...) and avoid the chance of the learner hearing overlapping audio by inadvertently revealing another numbered layer.

Hopefully that helps!

Yikes, let me try. Thank you very much.