Jesus called witness # 2 'FATHER'.
If witness # 2 was God, then Jesus was the Son of God - the Christian Record is true.
However, if witness # 2 is John, then the Jewish Law is true and the Christian Record falsified.
If the Jewish Law applies (Jesus was a Jew and he was addressing Jews) then John was the father of Jesus by the words of his own mouth, satisfying all the conditions and qualifications of the Messiah, in particular, being from the seed of David.
Christians argue that Jesus said: the Father. He did not say my Father.
So, to them (Christians), the Father means God Almighty.
Jesus was the claimant and the Pharisees were the challengers. How did they understood each other?
"Where is 'thy' father ?" (John 8:19)
'Ye neither know me nor my father, if ye had known me ye should have known my father also.' (John 8:19)