So, He used to have free will, but now He doesn't anymore, right?
Limited free will. He can choose between multiple good options but can never choose a bad option.
How then was Christ able to suffer temptation in the wilderness? The Immune System isn't stupid - in fact it is the Third Person of the supremely knowledgeable Godhead. For purposes of the Incarnation, the very same Third Person who
normally immunizes the Godhead against sin assumed the responsibility of disimpassioning the holiness of the incarnate Son to allow the possibility of temptation-on-earth. But isn't this an example of the Immune System behaving contrary to purpose? Not at all. The purpose of the Immune System is to preserve the Godhead. The incarnate Son was probably a mere paltry few particles of the unfathomably dense Godhead - any corruption there would not jeopardize the Godhead
as a whole. Far from being contrary to purpose, the incarnation afforded the opportunity for atonement (payment for our sins on the cross) thereby helping to
secure one of God's purposes - a bride for Himself.
By the way, let's summarize the Trinity. Maurice Merleau Ponty wrote a famous book named The Phenomenology of Perception. In that book he argued that the behavior of the human body cannot be explained in purely mechanical terms, rather it self-propels by free will and spontaneous intuition. For example a piano-player can quickly switch from a large organ to a smaller one even though the spatiality of the keys is different. Such a quick transition, he argued, cannot be explained in terms of consciously memorizing all the new angles and distances. Rather it is a kind of mechanistically inexplicable intuition, it is 'knowledge in the hands' (his words) and thus, 'the consciousness of the body invades the body, the soul spreads over all of his parts' (his words). He wasn't a Christian (he didn't mean the body has a soul in the Christian sense), in fact he was refuting Descartes' definition of a soul that localizes the soul to the head and thus reduces the rest of the body to a mere machine.
Descartes was unable to convincingly explain pain in the body - his view might be able to explain pain in the head (a headache) but not pain in the feet for example. The upshot of all this is that identity is an elusive concept. Which part of your body is the real you? Which cell in your brain is the real you? I am not a singleton but a multiplicity. Each part of my body engages in self-propelled acts of free will. I am multi-volitional. Given that such multiplicity is a fact of human experience, the Trinity is not a concept beyond human understanding.
With that as the backdrop, we can define the Trinity as three physical subsections constituting the Godhead. Man was literally made in God's physical image. The Father is a human-shaped figure, therefore, seated on a throne. The Son is likewise a human-shaped figure seated at His right-hand. The remainder of the divine Presence is the Third Person entitled the Holy Wind/Breath who, for example, issues forth by divine speech (note we generally exhale breath when speaking).