Audio layers mix up and previous/next

Hi Everyone!

I have a slide where the user clicks on different squares to learn more information on different layers. Each new layer has two audio tracks. The first one is what happens before the van/airplane is clicked on. Once it is clicked on, the other audio starts and the first audio stops. It works fine until you revisit the layer. Then, the audio gets weird after you click on the object. How do I make the second audio track go back to the original state when the layer is being revisited?

Also, a suggestion was made to make the next/previous buttons unavailable on the layers and only visible on the main base layer so that people wouldn't move on to the next slide accidentally. I don't really want to require the learner to click on all the layers if they don't want to, but I don't want them to do it accidentally either. I want them to be required to at least go back to the base layer, and then they can decide if they want to skip the other ones.

What would be a good strategy for disabling the previous/next buttons on the layers and not the main base layer? I hope this makes sense.