seventh psychopat (spoiler)

does anyone think that colin farrell is one of the psychopats?
why would they count sam rockewll as two of them but to leave an open discussion about farrell.when talking to tom waits at the end,he was clearly different person and why would tom waits just gave up killing him.

also,i didnt understand Vietnamese story.they are all different types of psychopaths.sam rockwell is a lunatic,woody is a cold blooded killer that cares more about a dog than people,tom waits and his wife are just addicted to killing and walken is a revengeful type with principles.
and can there be a reason why 7 of them?my first thought was 7 sins but i dont know...