@Mizumachi @Kryspy_Kreme
Don't forget that back in the day, the goal was to have as many children as possible (which is why harems became a thing in some cultures in the first place) because it was expected that at least half of the children would not live to the age of 5 anyway due to natural causes. Child mortality was rampant in the time before pre-natal care and as a ruler, you wanted to be as sure as humanly possible that you had at least one male offspring left to take over by the time you die.
Similarly, commoners had a lot of children too, especially farmers, as they were considered free labour and you had a higher chance of at least one of them being left alive by the time you are old so that someone could take care of you.
Now, having a lot of daughters meant you could increase political influence through strategic marriage (although they were expensive as each daughter was expected to come with a substantial dowry as compensation to the other family for having to feed the new useless birthing mashine -.-) and having a lot of sons was fine as well so long as the line of succession is clear. In many cases, having the sons kill each other for the throne is probably the least advantageous course of action, as the "winner" could still fall ill or die in battle and suddenly the kingdom would be left without a ruler. So unless two (or more) of the sons wanted the throne, in most cases the non-sultan/king/emperor sons would just become high ranking nobility and serve as back-up.
There was a time in which the sons fighting to the death was common, but, as you can imagine, that particular dynasty died out pretty quick hahaha