Two-book series/duologies seem to be gaining popularity in YA! Check out some of these duets! Except Treatment is a trilogy not a duet.
The Lunar Chronicles . Absolutely one of my favorites ! It's a clash of Disney princesses, Indiana Jones and Star Wars! Must read Marissa Meyer
"The Chronicles of Narnia" Book Set C.S Lewis
The Legend Trilogy Boxed Set: Legend/Prodigy/Champion [With Life Before Legend] [Book]
If you like the hunger games. start on this. The Maze Runner series by James Dashner. The Maze Runner, The Scorch Trials, The Death Cure, and The Kill Order (prequel).
Young adult series don't just have to be for teenagers. Here are 12 teen books for adults to read, too!
The Ruby Red Trilogy Boxed Set - Kerstin Gier, Anthea Bell
You have every book in the series proudly displayed in your house. 19 Undeniable Signs You're Obsessed With "The Mortal Instruments" Series