The leader of a faction runs it. They have the ability to demote/promote any member. They can kick any member from the faction, and they can even resign. The leader is in charge of keeping the faction in order and coming up with rules for the faction.
Essentially the leader's second-in-command, the director is usually a person who is trustworthy and a good friend (either in-game or IRL) of the leader. They will often enforce the rules, and basically just run the faction when the leader is not around. The director can promote/demote, and kick from the faction any member except the leader. They can add people to the faction, grant titles, and change the faction slogan (which the leader can also do). There is only one director and one leader for any faction.
Marshals are 4 people you can trust who can promote/demote Commissioners/Executors. They can also add people to the faction.
Their only ability is to add people to the faction. The max number a faction can have is 12 executors.