Fate of the Jedi

The Fate of the Jedi Series
Forty years after Return of the Jedi, the Skywalker and Solo families struggle to recover from unspeakable tragedy, even as their own government has turned against the Jedi. But there are bigger threats to face: A long-lost Sith tribe plots to overthrow the Alliance, even as a mysterious ancient power drives young Jedi insane before threatening the galaxy with an apocalyptic purge.

The backstory of the Sith group in this series is told in the book Lost Tribe of the Sith. Consider reading that book first to better appreciate parts of Fate of the Jedi, or reading it afterwards if you want to learn more.

Buy from Amazon:
Outcast by Aaron Allston
Omen by Christie Golden
Abyss by Troy Denning
Backlash by Aaron Allston
Allies by Christie Golden
Vortex by Troy Denning
Conviction by Aaron Allston
Ascension by Christie Golden
Apocalypse by Troy Denning

This is a post-Return of the Jedi series from the Legends timeline. Think of it as an alternate universe from the sequel movies and newer books.