This is the problem with systematic theology. They try to understand the infinite (God) with a finite mind, reasoning.

That means it's an idol. What is true, what is real is the Word of God. Jesus was God in the flesh, but also the only Begotten from the Father (the Son). His true essence is of the Holy Spirit. The Bible teaches us this.

But, we are also reborn of the same Holy Spirit. Meaning our eternal essence is of God Himself. Therefore Christ is not God's only Child, we are all Children of God if you are reborn of the Holy Spirit.

This is what a literal reading of the New Testament yields. Theology then puts that through a grid forcing the reader to interpret the scripture in a certain way.

There is the Father, the Son, the Holy Spirit and the Body of Christ. We are part of the Body of Christ. We are Royalty. We are God's family as reborn Christians.