"God Is unique ...if He starts having family then there is no difference between the creator and the creation."This is an astute question as it acknowledges that God is unique and we expect Him to be different from ourselves. One of the greatest difficulties we face when trying to understand God is in trying to understand Him in human terms. Here we try to understand God and the Son of God in human terms of having children and starting a family. Though we call Him the Son of God it is not as if God one day decided to take a wife and start having children. My reader correctly surmises that if this were the case then God would no longer be unique and no different form the rest of His creation. To properly understand what is meant by the term "Son of God" we must first understand this term in its context.
Often the scriptures use the same term to mean multiple things, each which must be understood by its context. For example, what the scripture means by being born or begotten is different based on its context. When the scripture says that "Abraham begot Isaac, Isaac begot Jacob, and Jacob begot Judah and his brothers." (Matthew 1:2 NKJV) it means that Isaac, Jacob, and Judah were born of natural means with a father and a mother. When the scriptures speak of Jesus saying "And the Word became flesh, and dwelt among us, and we saw His glory, glory as of the only begotten from the Father, full of grace and truth." (John 1:14) It does not mean that Jesus was born in the normal human since but that the Word of God was incarnated in human flesh in the womb of the virgin Mary. And, when the scripture says that Jesus, "is also head of the body, the church; and He is the beginning, the firstborn from the dead, so that He Himself will come to have first place in everything." (Colossians 1:18) it is obviously not speaking of normal child birth or the production of a human family since no one has ever created a family by giving birth from the dead.
Similarly, when Jesus is call the "Son of God" we do not take the term "Son" to mean and stand for normal sons and daughters as we might have them. The scriptures speak of Adam this way, "the son of Enosh, the son of Seth, the son of Adam, the son of God." (Luke 3:38) Although Adam was in no way birthed as normal children, yet he is called the son of God because he was directly made and fashioned by the hands of God. Similarly, Job refers to the angles as the sons of God, not because they were birthed, but because they were created. "Now there was a day when the sons of God came to present themselves before the Lord, and Satan also came among them." (Job 1:6) Also, believers are called the children of God, not because we are born so but because we are made so by the salvation of God. "But as many as received Him, to them He gave the right to become children of God, even to those who believe in His name." (John 1:12) So Jesus is called the Son of God, not because He was made or because he was birthed, but because He came from the Father and entered this world through the womb of a virgin.
Finally, we must realize that, even as Jesus was born into this world, it was not as if He never existed until His birth. Jesus told this parable of Himself and His mission on Earth.
"At the harvest time he sent a slave to the vine-growers, so that they would give him some of the produce of the vineyard; but the vine-growers beat him and sent him away empty-handed. And he proceeded to send another slave; and they beat him also and treated him shamefully and sent him away empty-handed. And he proceeded to send a third; and this one also they wounded and cast out. The owner of the vineyard said, 'What shall I do? I will send my beloved son; perhaps they will respect him.'" (Luke 20:10-13)Here, Jesus shows us that when He was sent from the Father to enter this world as a child, that He already existed with the Father. Jesus' birth was not His creation. He was from eternity with the Father and will for all eternity continue to be with the Father. John says, "In the beginning was the Word, and the Word was with God, and the Word was God... And the Word became flesh, and dwelt among us, and we saw His glory, glory as of the only begotten from the Father, full of grace and truth." (John 1:1, 14) John clearly states that Jesus always existed with God as the Word of God and was, in fact, God. His coming forth as the Son of God was his appearance upon Earth but not His creation as the Son. Paul writes of Jesus, "He is before all things, and in Him all things hold together." Things that can only be said of God. Similarly, "who, although He existed in the form of God, did not regard equality with God a thing to be grasped, but emptied Himself, taking the form of a bond-servant, and being made in the likeness of men. Being found in appearance as a man, He humbled Himself by becoming obedient to the point of death, even death on a cross." (Philippians 2:6-8) Showing clearly that Jesus existed as God long before He ever became a man and walked among us.
I hope this helps you to understand Jesus as the Son of God and His incarnation into this world.