6 decades books

Twins Zaphyr and Zull Tyrill never expected anything more out of life than to learn the art of hemomancy - manipulating blood with their mind - and to serve as healers in their home port of Varin. However, their life is overturned when they must deliver a mysterious letter to the Empress, all while a mysterious enemy tries to stop them at every turn. An array of mad killers and criminals stands between them and their goal, and if the twins are to survive they will need their skill, their wits, and perhaps the help of some very unlikely allies...