Blood and Venom by Isabel Wroth

Erufir has been a fugitive, a slave, and through an ironic twist of fate becomes a science experiment. As he waits alongside his blood brother for the testing to begin, he is baffled when Zyre suddenly begins talking to himself.
In the darkness of the lab, the ephemeral figure of a female ghosts back and forth, tormenting the crazed scientist, Reykar. At first, Zyre seems to be the only one able to see or hear the female, but soon enough the beautiful apparition finds a way into Erufir’s dreams and convinces him that though she’s technically dead, she’s as alive and real as can be.
Her body was destroyed long before their arrival, but if they want to resurrect the female meant to be their mate, the brothers must return home to make a dangerous bargain.
A life, for a life.