Do any of you remember a book series from 1990's (possibly) with 10-15 books about a supernatural family (not immortal) who have a sibling feud that leads to a war.
One scene takes place on a narrow one person bridge and the armies are waiting at each side.
The author also did the audiobook narration of the series.
This sounds like Roger Zelazny's 1970 Nine Princes in Amber, in which mystical (able to walk between different realities, amazing healing powers over the long term, sometimes actual sorcerers), yet not immortal brothers and sisters feud for succession leading to war. There is a scene in a narrow bridge, pass, or stairs (to me a little reminiscent of the battle of Thermopylae).
Nine Princes in Amber was the first of a series of five books, followed by another series of five books about the next generation within the family). Zelazny recorded audiobook versions himself in 1990, despite not being a professional voice actor.
Nine Princes in Amber (and its sequels) has been published many times, but here are some paperback covers:
