The "triune God" is a clerical error. "Trinity" does not exist in the Bible.
Compare KJV with NCV for 1 John 5:7–8.
A footnote in NCV explains the problem: "A few very late Greek copies and the Latin Vulgate continue, 'in heaven: the Father, the Word, and the Holy Spirit, and these three witnesses agree.'"
God is the Father of it all. Jesus is one Son of God, and we can all be Sons of God, if we each awaken the Holy Ghost in ourselves -- the True Self (the child of God who was created in His image).