Update: I implemented inheritance for the Humours, Sins&Virtues. I won't really test them now, we'll have to see if they feel right in the real test games later.

Another point I wanted to mention: The humours will have five trait levels (well the Sins/Virtues, too) - however the player won't see which level his characters have.
This is meant to represent that you won't exactly know how far a person does indeed tend towards that humour - in the real life you normally don't know this about other people, either. What you will get to see are the secondary traits and you should be able to make an educated guess about how far they are going into a certain direction, but you won't know for sure.

I'm currently thinking to use that system for each multi-level trait that describes a more private part of the character's personality which would not readily be apparent in real life, either. For me this will definitely enhance the role-playing aspect of the game.