No there is not only One Son of God. The greek word for the baptised Jesus in the Jordan is "Huios" and God says, My Son in whom I am pleased. This word "huios" is used many times in the N.T. when referring to Holy Spirit filled followers of Jesus Christ. Though we may be sons (huios) of God, not many are "manifested" sons of God...but since Creation is waiting for it! Do some word study and meditation. The Truth will come to you.