Will insert my 5 cents. IMO ingame islam should be singular religion broken apart by traits. After all during much of the period generic population of the muslim world frequently was changing its "owners". Shias, sunnis, kharijites... who cares, farmer has a work to do and mouths to feed. Commoners had no say and no interests in affairs ( at least not religious one ) of muslim aristocracy. Making them whole will solve current issue with muslim anachronistic "heresies" and open up possibilities for certain character to rise up with their own branches of islam ( various mahdis ) or claim to be caliph of existing branch ( umayads vs abbasids ). After all various muslim sects in most of the cases were rivaling each other either because of power disputes ( who is the real caliph? ) or because of petty theological differences. Islamic shcisms unlike christian ones did not sported different power structures and islam itself never had church like vertical organization.
Concerning the bolded part:
1) How is in this aspect Islam different of Christianity? The farmers etc. didn't really care in neither religion. They just did what was the custom. That's why they were often reluctant to convert to either religion, be it christianity from paganism, islam from paganism, islam from christianity and vice versa or any other situation.
2) Anyway, this isn't really relevant at all since this game isn't really about farmers and commoners, but 90% of the characters are nobility. So?
OTOH I you are indeed correct that the theological differences weren't that big between various muslim branches (though I'm not really expert on religious affairs), definitely not as big as between christian branches. Concerning what you wrote, the situation was very similar in Europe - the farmers usually didn't really care.
The division was largely driven out by political reasons and concerns and was a case of rulers and nobles. There were of course exceptions and I would say (to oppose both your and my own claim) that the city craftsmen, minor nobility etc. were often very pious followers of whatever religion, because it was what bore their ethical code.
But while this game is mainly about nobility and the changing religious affiliations were often a political, rather than theological issue, it is perfectly fine that both Islam and Christianity are divided.
How it is done and that it should be done much better, especially in case of Islam, is another thing.
BTW this concept is mainly about social and cultural ways to enrich islam, since I'm not an expert on religious issues. However I can only repeat that I welcome all inputs about how also religious aspect of Islam could be improved. But to be honest, I don't really think that making it a monolith would be actual improvement.
Islam had more and deepr differences which can barely be simulated by personal traits. It had specific mechanisms which were different in each branch. The game could actually somehow have some mechanics which would simulate the differences between various madhabs etc.
Why did you remove two of your posts on June 6?
There were quite a few factors playing role in it and some of them should better remain secret. So while I believe it would be better not to comment your question at all, I believe you deserve some answer. Unfortunately I can't say much about it, sorry