Princes of the Blood Series by Megan Derr

In a kingdom ravaged by the beasts and terrors of an ancient war, the only hope against them is the army of mixed-blood beings known as the King's Legion: dragoons, shadowmarch, sorcerers, titans... and the Princes of the Blood, nigh-invincible warriors of fearsome magic and strength, their only weakness a need for pure human blood. When his brother runs away, Raffé agrees to undergo the Blooding, but he is a pale imitation of his strong, capable brother... moreIn a kingdom ravaged by the beasts and terrors of an ancient war, the only hope against them is the army of mixed-blood beings known as the King's Legion: dragoons, shadowmarch, sorcerers, titans... and the Princes of the Blood, nigh-invincible warriors of fearsome magic and strength, their only weakness a need for pure human blood. When his brother runs away, Raffé agrees to undergo the Blooding, but he is a pale imitation of his strong, capable brother. No one expects him to survive and become a Prince, merely to die to save the rest of his family and preserve honor. But runaways and weaklings are the least of the kingdom's concerns when an ancient evil returns with new tricks, and their only hope lies with knowledge long lost and a fierce bond forged in darkness... less

When his sister falls ill, Kristof is ordered to assume a duty never meant for him: become the Duke of Stehlmore and marry a notorious Prince of the Blood. It is one of the oldest honors and duties undertaken by his family, but Kristof feels only resentment that he must leave behind all he knows to serve an arrogant half-demon... moreWhen his sister falls ill, Kristof is ordered to assume a duty never meant for him: become the Duke of Stehlmore and marry a notorious Prince of the Blood. It is one of the oldest honors and duties undertaken by his family, but Kristof feels only resentment that he must leave behind all he knows to serve an arrogant half-demon. His resentment must be set aside, however, when evil is found lurking far too close to the castle—an evil that has many pieces, controlled by someone they cannot find and who always seems one step ahead of them. Someone who seems to think that demons are little more than toys ... less

Prince Telmé Guldbrandsen has been groomed since childhood to become a Prince of the Blood and Commander of the Legion. He will be the youngest person to ever take the Blooding—if he can behave long enough to prove he can be trusted with the responsibility. But behaving is difficult when he is constantly forced to endure Korin: heir to the Reach of the House and the Temple of the Sacred Three, and the snotty brat Telmé is expected to someday marry... morePrince Telmé Guldbrandsen has been groomed since childhood to become a Prince of the Blood and Commander of the Legion. He will be the youngest person to ever take the Blooding—if he can behave long enough to prove he can be trusted with the responsibility. But behaving is difficult when he is constantly forced to endure Korin: heir to the Reach of the House and the Temple of the Sacred Three, and the snotty brat Telmé is expected to someday marry. Then the unthinkable happens, leaving Castle Guldbrandsen—and the Legion—in pieces. Overwhelmed by fear and grief, Telmé convinces Korin to help him attempt the impossible. But rather than relief, Telmé's triumph is met with anger and rejection … less

Fifteen years ago, several wolf pups were kidnapped by poachers to be illegally sold abroad. They were rescued by a Prince of the Blood, and the Wolves of the Moon vowed the debt would someday be repaid. Now of age, wolf Ilkay Thrace is determined to fulfill that vow. Before he can, though, the Wolves' home high in the peaks of Dragon Claw Mountain is ravaged by an earthquake that reveals an ancient, forgotten temple—and awakens something dark and terrible in its depths... moreFifteen years ago, several wolf pups were kidnapped by poachers to be illegally sold abroad. They were rescued by a Prince of the Blood, and the Wolves of the Moon vowed the debt would someday be repaid. Now of age, wolf Ilkay Thrace is determined to fulfill that vow. Before he can, though, the Wolves' home high in the peaks of Dragon Claw Mountain is ravaged by an earthquake that reveals an ancient, forgotten temple—and awakens something dark and terrible in its depths. Now, instead of repaying their debt, the Wolves must once again ask the King's Legion for help.Despite the time that has passed since the Legion was nearly wiped out, their greatest strength, the Princes of the Blood remain few. It is one of their newest, Prince Dalibor, who is sent to evaluate and assist the Wolves. But Dalibor is born of a demon of wrath, his greatest power the ability to drive all living beings out of their minds with rage and fear. He is brash, loud, and reckless, even by the standards of the Legion, and the very last person that should be going into dark, treacherous caves containing ancient evil. less