Yes, family history is considered IC knowledge.
The OP stated that he desired the name of the assassin to be added to the victim's family history, and the name of the victim to be added to the assassin's family history: "b) your character's death would be writen in your family history along with the killer's name/ also your character's name would writen in the family history of the killer"
There are many cases where the name of the assassin is never discovered, or the wrong person is blamed. How would anyone know who really did it? And if you were never identified, how would anyone know to blame you, so as to record it in your family history? Adding it to family history would be a horribly meta-gamey piece of information. It would be much better to simply tag the victim's history with "Slain by an unknown assassin".
I'd accept that line of thought. I'd always known that family history is IC and publicly available, but I've always found it tedious to get to (which I assumed was purposeful). I like the unknown assassin concept as a replacement.
