I recently read/listened to two books with a similar premise: the royal family has been killed and treasonous interlopers have taken over the kingdom, only --------- can save the kingdom. The first of these novels is The False Prince by Jennifer Nielsen. The second is Finnikin of the Rock by Melina Marchetta. The first I enjoyed enough to continue to the second book, The Runaway King, the second I did not.
The False Prince stars Sage, an orphan/street kid who is taken away by a man who needs to find a boy of the right age to impersonate Jaron, the missing prince in order to save the kingdom from chaos at the hands of power hungry regents. Sage, Roden, and Tobias will spend time training to become Jaron. Whoever best does so will return to Carthya to become king. The other two will in all likelihood be killed.
Ten years ago, the kingdom of Lumatere was attacked from within and the royal family wiped out. A sorceress's curse has prevented the restoration of Lumatere. The story begins as Finnikin, the son of the former captain of the guard, along with Sir Topher, the former king's first man, and Evanjalin, a religious novice seek to break the curse by finding Balthazar the heir to the throne.
For me, The False Prince was a much more exciting story with a fast pace. Because of this I was interested to read the second book (and probably the 3rd) to find out how the kingdom fares with its new king. I will not be reading Froi of the Exiles to find out about Lumatere. Marchetta has a very heavy hand with the "power of the mysterious goddess" blabbity blab. I call this the Red Tent effect. I read The Red Tent when it was all the rage. I hated it. Let me be clear, I am all for the acceptance/belief/realization of the blow to women's power that came in with the rise of patriarchal Christianity. However, I do not need nor want a novel to shove female mysticism and strength down my throat. I feel Finnikin of the Rock did this in excess; it simply felt preachy. I have asked one of my male students to read it because my adult perspective is often put off by elements of a book that kids either do not see or see differently.