What you need:
Slider 1 and Slider 2 are controlled by Slider 3. Slider 1 moves slower (range is bigger) than Slider 2. That creates the parallel effect. Use a fade-in, fade-out extra object to simulate darkness when Slider 3 approaches the end. Done.
Here’s more unparalleled parallels:
https://community.articulate.com/articles/using-sliders-to-create-parallax-effects
