Every Muslim ruler should learn topiary. Well-trimmed family trees make life much easier.
I honestly now believe you need to have civil war between family and imprison and execute your evil brothers and half brothers, to keep the dynasty as small as possible!
Only read the OP so someone have probably said this already. But, Do not give land to your family members, they will just breed like rabbits and make your decadence rise really fast. Let your sons have the counsil positions, the rest you imprison and/or kill. In the few games I have played as muslim my decadence have never been higher than the starting level.
I agree it is a wierd system, but I have heard it was common practise in the ottoman empire for brothers to imprison eachother so there would be no succesion crisis, of course not normal prison, more like a fine room in a palace. Dont know if any other muslim dynasties did that though.