Yannick is a murder freak because no other form of self-actualization was ever available, safe or effective to him. He establishes his position in the world by the means of violence at bigger and bigger scale. He does not enjoy the act itself and can delegate it so someone else, save for the really important, personal targets. It is the most assured way to get the job done correctly, but it doesn't have to be him.
(does it?)
Eloise is a murder freak because violence is an efficient tool of exposing a person's core to her. To push someone to violence or to inflict it upon someone makes it easier to see them in their barest, most honest form (to her). She does enjoy the act in its rawness and pure brutality, but any other way that accomplishes it is just as good to her.
(is it really?)
Leikki is a murder freak because violence is a ritual to be reveled in. If done correctly it brings them closer to their god's essence, but it must be staged, performed, witnessed. Otherwise it's just a butchery, a domain of beasts, and they are not a beast - they are a faithful servant who enjoys the act only as far as it is demanded by the deity.
(is it demanded?)
