Answer: God has many sons, but only one “only begotten” son.
Perhaps the best approach would be to discover “how” one is made a son. The first and most obvious answer is that one is made a son by birth, when a father brings a male child into the world, as in Adam being the son of God (Luke 3:38). Adam’s also had children: Abel, who was pleasing to God and Cain, who displeased the Lord by keeping a hard heart. After Cain killed Abel, Adam had another son (Seth) who was pleasing to the Lord. The descendants of Abel (“sons of God”, nobility) took wives from the descendants of Cain (“daughters of men”, peasantry) as described in Genesis 6:2-4.
A second option would be that one is made a son by adoption. This is how “son” is applied to the Christian. “But as many as received him, to them gave he power to become the sons of God.” (John 1:12) because “He predestined us for adoption as sons through Jesus Christ, according to the purpose of his will” (Eph 1:5).
But what about these other “sons of God” such as those who witnessed Creation (Job 38:6-7) and who presented themselves before the Lord (Job 2:1). We should ask: are these sons Christians, sons by adoption? Clearly, no. Are they beings who share a common source, a father? Clearly, yes. Are they human? Clearly, no. They must be spiritual beings.
Where does this leave us concerning our final option, Jesus, God’s only begotten son (John 3:16)? Reviewing the list above, no other son is described as “only begotten” except Jesus. There is only one only begotten son, and that usage has a clear definition: the son who God raised from the dead. "God has fulfilled this for us their children, in that He has raised up Jesus. As it is also written in the second Psalm: 'You are My Son, Today I have begotten You.'" (Acts 13:33)
Therefore, "He who believes in Him is not condemned; but he who does not believe is condemned already, because he has not believed in the name of the only begotten Son of God." (John 3:18)
“In this the love of God was manifested toward us, that God has sent His only begotten Son into the world, that we might live through Him.” (1 John 4:9)