why can't there be multiple intellects in one being that is to say God?

Salamu a3laykum,I am a convert to maturidi sunni islam from orthodox christianity.I am trying to complete my imaan,and I am seeking out logical arguments for Tawheed.I have been making du'as to Allah Ta3ala to guide me to tawheed and I have found many arguments for tawheed from various philosophers like karlo broussard,ibn sina and Plotinus.I found this(1) from Thomas Aquinas(2) on why there can be only one being who's essence/being/nature is it's existance and must be (I presume numerically,and not composite)one.but why must this being be numerically one like in islamic Tawheed instead of a composite one?why can't it be composed of multiple intellects as the christians assert?and are there any other reasons there can't be multiple beings with their essence as their existance,like the polytheists assert?for anything that doesn't have its essence as its existance is of course created. any help would be appreciated! 1.A being whose essence is its existence could not be multiplied (i) through the addition of some difference, for then its essence would not be its existence but its existence plus some difference, nor could it be multiplied (ii) through being received in matter, for then it would not be subsistent, but it must be subsistent if it exists in virtue of what it is. Overall then, if there were a being whose essence is its existence, it would be unique, there could only be one such being, in all else essence and existence are distinct. 2.Latin Trinitarians are Modalists and don't believe in the social trinitarian tritheism of other christians.they believe that the son and spirit are numerically identical with the father thus are monotheists albeit imperfect ones(because then the son and spirit are merely events in the father and events don't have will or action)