So I got my hands on the Sword of Islam DLC and the dynastic politics of Islamic nations is insane.
So for everyone out there who doesn't know here's my guide to how everything works.
So Muslim rulers have a minimum wife requirement thing, I've only been a Emir(Duke) and Sultan(King) so far but it seems to follow a pattern of 2 for a count/sheikh, 3 for a Duke, 4 for a King, 5 for an Emperor, for every wife you have below the wife requirement you lose 1 prestige every month, for every wife over you gain 1 prestige, there seems to be a limit on how many wives you're allowed to have at once, but I haven't really experimented with that yet. So, I hear you wondering, what's to stop me taking as many wives as possible to rake in that extra prestige? Well, nothing, except that the more wives you have the more they'll tend to stir up trouble.
See, while some Muslim rulers start out with gavelkind, or open elective succession, Muslims default to Turkish succession, and while they can all switch to Turkish succession, they can't seem to switch out of it without swapping religions.
Turkish succession is where the strongest son (the son with the most titles) inherits everything and all immediate relatives (such as uncles, brothers, and half brothers) will get a strong claim to the throne. Fortunately Muslims rulers get to imprison any relatives that are not their son, so if you have any relatives with land that can try to rebel you can immediately try to lock them up.
To top everything up there's decadence to deal with. See, every Muslim dynasty gets a decadence score that's raised by decadent relatives, as near as I can figure decadent relatives are male relatives that are sitting around the palace smoking hashish and eyeing up your wives, the mixed aura of impertinent rage and hashish smoke make your realm run worse and worse, it loses you tax income, worsens relations, and causes bad events. Whatever you smoke or eye up has no effect on decadence, it's just your sons, cousins, brothers, etc. that cause the problem.
There are a few different ways to take care of these relatives, first is just imprisoning them. You can imprison any relative that isn't your son, and only the parents will care. If they escape and run away to another realm they're someone else's problem (until that someone else uses their claim to declare war on you), if they have lands and they rebel you get to kick their arse. You still get a tyrant penalty if you try to imprison your sons, so you have to either assassinate them, make them your strongest son(being heir seems to take away decadence), or give them a position on the council. I thought that giving them lands would stop the decadence, but that apparently doesn't work.
You can lower decadence by having a very small personal demesne, giving land to dynasty members (this is a bad idea), fighting battles and sieges, and paying to throw a special feast for ramadan, the Muslim version of lent.
You'll notice I didn't talk about daughters much here. That's because daughters are largely irrelevant in all this, Muslims are stuck in the women never inherit mode, and there's no such thing as a matrilineal marriage for them. Which means they really are only ever useful for marrying off for an alliance.
Well that was a very lengthy explanation, did I miss anything?