The Bone Doll's Twin, Hidden Warrior and Oracle's Queen, all by Lynn Flewelling, have an unusual premise for your standard Training of the Fantasy Prince trilogy. Prince in question is actually a princess who, through the help of necromancy suffered shortly after birth, has appropriated the body and likeness of her dead twin brother.
Watched over by the three magicians who did the morally questionable deed, Tobin is raised as a warrior prince, haunted by the alternately vengeful and protective spirit of his dead sibling. Things get even messier when Tobin learns the truth about his identity. In books 2 and 3, he comes to terms with his true identity as Tamir, future queen, his relationship with his faithful squire Ki and his family-sundering war against his cousin to gain the throne.
Utterly lacking in suspense and subtlety, this trilogy nevertheless interests you with swift plotting and able management of a large cast. I especially appreciated the fact that, for a book that was largely about battle, the chapters focused less on the minutiae of maneuvering and more about the characters' physical and mental experiences. This same attention to psychology fell away, however, when Flewelling focused on Tobin/Tamir's sex change and the dead brother. Though Tamir went through the expected doubt and discomfort, I never really saw her reconciling her past as one sex with her present as another. When her usurping cousin accuses her of being "a mad boy in a dress," shouldn't that prompt some ambivalence, defensiveness and reflection on her part? Tamir was not a particularly reflective character, but surely she's got to have some sort of self-justification going on, right? Or maybe she doesn't really have a problem switching sex because her hardened, war-like, aggressive gender presentation doesn't really change? I wouldn't know. We never really got the answers. Disappointing.
The same with Tamir and her dead brother. Though we see outward displays of ambivalence and grief, the creepy fact of being stalked by someone whose skin she stole doesn't really affect Tamir's mind. In fact, Flewelling kind of cops out by having a magician reach into Tamir's mind and literally sever ties between her and her dead family members. Because a wizard breaks the bonds between Tamir and her dead brother, we lose an important chance for insight into how she makes peace with her shadow self.
On the level of an adventure fantasy, this trilogy works well. High points include universally appealing characters and an appealingly matter-of-fact treatment of both magic and ghosts. As a ghost story and/or a transgender story, the trilogy, for all its interest in matters ghostly and transgender, doesn't do so well. While making central the subjects of spirits and transgender identity, Flewelling ultimately uses them as unusual, skillfully rendered, but uninsightful, plot points. Good fantasy.