Oooh, 'realism'? Don't think so. Primogeniture, which is a lovely word, wasn't really introduced until at least the end of the telfth century. Up 'til then it was whoever had the biggest sword/whoever could gain and hold on to power. This would sometimes mean a son/brother succeeded, but this was coincidence.

This is just intended as an historical footnote, not CA- or anyone else-bashing. I realise they have to play to popular culture, etc. So there.