At this time, the Persian empire was so decadent and corrupt, that it’s easy to see why Islam (technologically inferior in most ways) was able to defeat them.
Don’t know if it’s true. I read the Turks had a way of selecting their new ruler if there were multiple males. At close to the time of the old age of their father they would all be Put a gilded cage (guess that means a locked up wing of the palace).
The one that came out alive would be the ruler.