The Black Fleet Crisis trilogy by Michael P. Kube-McDowell
The remnants of the Empire have retreated and the galaxy is experiencing a period of peace. Han, Luke, and Chewbacca finally have some time to dedicate to themselves and their families. But Leia, now president of the New Republic, must grapple with the political maneuverings of a ruthless regional leader whose machinations threaten to tear the galaxy apart. Meanwhile, Luke is drawn off on a wild goose chase in search of knowledge of his mother, and Lando investigates the secrets of a mysterious and ancient ghost ship.
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Book 1: Before the Storm
Book 2: Shield of Lies
Book 3: Tyrant's Test
This is a post-Return of the Jedi series from the Legends timeline. Think of it as an alternate universe from The Force Awakens and newer books.