Branching - How to show "Next" button only after branches have been completed

I'm inheriting a slideshow that has some basic branching. Basically on one slide (call it "Branch Slide") there are 2 buttons. Each button takes you to a scene. The "Next" button doesn't appear when first viewing the "Branch Slide". So users must click the 2 buttons and view the slides in their respective scene. At the last slide in each scene the "Next" button returns them to the "Branch Slide " I want to have a "Next" button appear on the "Branch Slide" after the users have completed both scenes. 

I've done some research and understand the basics about variables. But I'm unclear how to reveal the "Next" button in the player when 2 variables have become "True".