This story is a sequel to Naborale

When Rainbow Dash stumbled upon the hidden desert estate of Star Swirl the Bearded and his family while scouting for a new Wonderbolts training course, she thought it would just be a quick stop. Instead ,she found herself being recruited to fix a blackout and keep an eye on Star Swirl's precocious daughter, Nyx, while Star Swirl goes to some other world to fetch parts for a broken machine.
One mysterious earthquake later, Nyx has disappeared and what few clues can be found point to her being kidnapped and taken into one of the book worlds where Star Swirl's former apprentices, Cirrus and Archeon, had been sent to atone for the crime of destroying most of Star Swirl's research into alternate realities. With Spike at her side, Rainbow Dash must enter the prison worlds of Monolith and Ka'utani to search for Nyx, the apprentices, and the solutions to a whole new gauntlet of puzzles.

This story is a sequel to Sohndar

When Star Swirl the Bearded's wicked apprentices Cirrus and Archeon had ended their campaign of looting, murder, and destruction across the worlds Linked to Aitran Island, there were more intact books than were uncovered by Twilight Sparkle and Rainbow Dash. One of those books is I'strukun, the link to the first in a network of worlds intended to instruct Star Swirl's apprentices and daughter in the principles behind Writing links to other worlds. When Nyx insists she be allowed to take the lessons and Star Swirl admits his fear that Cirrus and Archeon may have caused great destruction to the worlds, Twilight and Spike accompany Nyx and take a look around.
Sequel to Aitran and Sohndar

This story is a sequel to Aitran

Twilight and Rainbow are asked by Star Swirl the Bearded to take on the challenge of finding his lost wife and daughter in the decaying world of Sohndar, which is ruled by an old enemy of Star Swirl's family who has been trapped there for uncounted years. Although their adventures in the worlds of Aitran have given our heroes the confidence to succeed, they'll soon find that Sohndar is an entirely different bale of hay.

Image by Muffinsforever

Twilight has discovered a strange old book purportedly written by Star Swirl the Bearded, and Rainbow Dash discovers a latent spell in it that transports the two ponies to a strange island in the middle of nowhere. With no viable options available to them, Twilight and Rainbow begin to search the island for clues to a way home and the reason behind the odd puzzles and contraptions presented to them.

Dramatic Reading here.