Merciless Stars by Candace Robinson

 Two sisters, as different from each other except for the magic and love that bind them. When emissaries from a neighboring kingdom attack the sisters, you're slaughtered on site. But why attack the target of a marriage proposal to unite the two kingdoms.

 The younger sister uses dark magic to steal a soul to bring a wax raven to life, while her sister sets it out to discover what is happening in the next kingdom

To deal with the threat, ancient myths must be explored to find a cure for both kingdoms or all is lost. But can they can make the ultimate sacrifice without destroying them all.

The author once again creates a magical world for readers to lose themselves in. Dark magic, savage appetites, a love that will sacrifice everything.