Is Jesus the only son of God?

We are all literal children of God, our Heavenly Father, and Jesus Christ is our elder brother.

Ye are gods, children of the most High, Ps. 82:6.

We are the offspring of God, Acts 17:29.

Be in subjection unto the Father of spirits, Heb. 12:9.

I am a son of God, Moses 1:13.

https://abn.churchofjesuschrist.org/study/scriptures/gs/sons-and-daughters-of-god

This is where understanding of the biblical Greek phrase, about Jesus being "the only-begotten" Son of God is important. Sadly, some modern translations of the Christian Greek scriptures have watered this down, by replacing that phrase with "God the One and Only" (NIV) or "the only-begotten god" (NWT with a small 'g') or "the only Son" (GNB) etc.

Older translations, like the Authorised Version, stick to the Greek text which has 'monogenes', applying to the Son (Jesus Christ), and so reading "the only begotten Son, which is in the bosom of the Father, he hath declared [God]." Notice the point about the position of the Son in relation to the Father? The whole verse speaks of the unique relationship of this Son to the Father. No other son of God is in the bosom [position - relationship] with God the Father.

That is because this only-begotten Son was never created. He is the eternal Son by virtue of "all the fulness of God dwelling in him bodily" as Colossians 1:15-19 shows. This Son was previously known as the Word of God, who was with God in the beginning, who IS God, and who made everything that was made - proving that he could not have been made (created) himself. That is the uniqueness that John 1:18 enlarges on. If you don't take the first 17 verses of John chapter 1 into the reading, the meaning of verse 18 will remain obscure. And especially so if you use modern translations, which detract from the unique relationship of this Son with God the Father.

The relationship that the many other sons of God enjoy is different to that of the only-begotten Son. Angels are called sons of God, but although they enjoy being in the very presence of God in heaven, they are created sons. Likewise with human sons of God. All humans are created by God and could be said to be 'sons' in that sense, but the Christian Greek scriptures speak of how repentant ones who have faith in Jesus become adopted into God's heavenly family. "Beloved, now are we the sons of God, and it doth not yet appear what we shall be: but we know that, when he shall appear, we shall be like him; for we shall see him as he is." 1 John 3:2. John was addressing that to fellow-Christians who were expecting the return of the Son of God in great glory, to transform them with resurrection bodies, to be with him forever.

This means that the answer to your question is that Jesus is the uniquely, singularly uncreated Son of God, the eternal Son, which can never be said of all the other sons of God. John 1:18 (when translated accurately) brings out the unique relationship of Christ (as the only-begotten Son).

Romans 14:8 does not detract from this because that verse applies only to humans who have first become adopted children of God. The very next verse explains that those ones

"have received the Spirit of adoption, whereby we cry, 'Abba, Father!' The Spirit itself beareth witness with our spirit that we are the children of God." (Romans 8:15-16)

But prior to that miraculous adoption, they were NOT children of God. There came a point in time when God chose to adopt them as his children, unlike the eternal Son of God who was always in the bosom of the Father, from before the beginning.

The Scriptures make it clear that God has an only unique(μονογενής (monogenés) Son, named Jesus.

The definition in Greek for μονογενής (monogenés) in John 3:16, translating from the word “only begotten” means: “single of its kind”. Source: Thayer's Greek Lexicon STRONGS NT 3439: μονογενής

Christians, who are adopted Children of God differ from Christ in that Christ is eternally “unique” in His own right as God’s Son. See (John 1:1-18, 3:16-17, 3:35-36)

The term “sons of God” can also refer to angelic beings: “bə·nê ĕ·lō·hîm“, see (Genesis 6:4, Job 1:6). Genesis 6:4 has been debated on whether it’s the godly line of Seth or angels, but Job 1:6 is for certain about angels.

The ESV which says: “For God so loved the world, that he gave his only Son…”

Is in one sense true and accurate if not taken in the absolute sense, but in terms of a modern translation it’s best to see the distinction of that Greek word “monogenés” as prominent in our understanding.

The KJV or NKJV may better reflect the language of the original Greek with respect to the term μονογενής (monogenés).

1. Jesus is uniquely begotten from the Father, and so is uniquely the Son of God in that sense. See Luke 1:35

"The angel replied, “The Holy Spirit will come upon you, and the power of the Most High will overshadow you. So the Holy One to be bornd will be called the Son of God."

John 1:14

"The Word became flesh [i.e., Jesus] and made His dwelling among us."

John 3:16

"For God so loved the world that He gave His one and only Son"

2. Jesus also uniquely has the prophetic title of 'the Son of God'. See Psalm 2:7

"You are My Son; today I have become Your Father."

John 1:49

"“Rabbi,” Nathanael answered, “You are the Son of God! You are the King of Israel!”"

and Matthew 26:63

"Then the high priest said to Him, “I charge You under oath by the living God: Tell us if You are the Christ, the Son of God.”"

3. We can all be sons and daughters of God, but it is in a different sense. We are neither conceived directly by the power of God, nor have the prophetic title of 'the Son of God'. However, we are 'born again' or 'born from above', becoming new children of God in the spiritual sense ('led by the Spirit'). See John 3:3-7

"Jesus replied, “Truly, truly, I tell you, no one can see the kingdom of God unless he is born again.” 4 “How can a man be born when he is old?” Nicodemus asked. “Can he enter his mother’s womb a second time to be born?” 5 Jesus answered, “Truly, truly, I tell you, no one can enter the kingdom of God unless he is born of water and the Spirit. 6 Flesh is born of flesh, but spirit is born of the Spirit. 7 Do not be amazed that I said, ‘You must be born again.’"