Next button after Layers and button

I can't look at your file at the moment, but I think I can still help. 

Because the user remains on the same slide when they click the buttons, you can use the Visited state of those buttons to control the NEXT button. The trigger would look something like this: 

Note: I'm  guessing there's a trigger to disable NEXT when the timeline starts. That trigger will run every time the user visits the slide. Therefore, it needs conditions to prevent it from running after the user has finished the interaction. That might look something like this: 

• The conditions are connected with "or." That means the trigger will run if any of the conditions is met. So if any of the buttons haven't been clicked (≠ Visited), NEXT will be disabled. But NEXT will remain enabled if the user returns the to the slide after completing the interaction.

Here's info about controlling the NEXT button: TIP: Controlling the NEXT Button 101 | Articulate - Community