So I added a npc to the followers faction, but he always run away during combat. How do I fix this? I thought aggression is the value, but its not.

Confidence is the value. At least it was in previous games.

Confidence? At least in Oblivion it was.

i use getav confidence and the value is the same as other real followers. So perhaps its not confidence anymore?

EDIT: Nevermind, I had Rally cast on him when I checked it, silly me. It is confidence.

Does anyone know by the way how to make certain followers steal stuff or not complain about trespassing ?
I added one follower via the console and i gave her the same factions as Lydia had --- she still complains about stealing and trespassing. I dont get any bounty for it, but i wont be able to send her to steal things and i also cant talk to her while trespassing...

Responsibility I believe is the actor value for that... or it was in previous games.

Responsibility doesnt work anymore i am afraid

Make sure they are in the proper factions. Factions is what decides reaction to other factions. I believe vanilla companions all belong to a special player-friend faction, though I dont know what its called exactly.

Value you want is "Confidence" -- http://www.uesp.net/wiki/Tes5Mod:Actor_Value_Indices

We already tried that, mentioned it and that article is about Oblivion.

I was experimenting with Muiri and Hroki and neither of them ever gave me any complaints no matter what I was doing. I set aggression and confidence to max (again, I was experimenting).
The only real problem I had with them was when I parted ways with them, the settings were high enough that they went berserk and started attacking me and everyone else. Now, I set the levels back to default when I let them go... it avoids dead bodies all over the place.

I think it has more to do with their factions, tbh, that was very important in Oblivion.

For stealing and etc it should still be responsibility from the appearance of the NPC files.