You would need to explain what you mean by "separate witness."
John 5:31 If I bear witness of myself, my witness is not true.
John 7:18 He that speaketh of himself seeketh his own glory: but he that seeketh his glory that sent him, the same is true, and no unrighteousness is in him.
John 8:17 It is also written in your law, that the testimony of two men is true.
Now combine the elements of what makes a false witness from a true witness and e see this happen at Jesus's water baptism.
Matthew 3:15 And Jesus answering said unto him, Suffer it to be so now: for thus it becometh us to fulfil all righteousness. Then he suffered him. 16 And Jesus, when he was baptized, went up straightway out of the water: and, lo, the heavens were opened unto him, and he saw the Spirit of God descending like a dove, and lighting upon him: 17 And lo a voice from heaven, saying, This is my beloved Son, in whom I am well pleased.
What Jesus meant in Matthew 3:15 was the fulfilling of the prophesy in Isaiah where the Lord God and His Spirit sent God Our Redeemer.
Isaiah 48:16 Come ye near unto me, hear ye this; I have not spoken in secret from the beginning; from the time that it was, there am I: and now
the Lord God, and his Spirit, hath sent me. 17 Thus saith the Lord, thy Redeemer, the Holy One of Israel; I am the Lord thy God which teacheth thee to profit, which leadeth thee by the way that thou shouldest go.
The Bible never says that the Father's will is not the Son's will or the Holy Spirit's will. They all will the same thing and work in unison to bring it about.
Jesus in His prayer in the Garden of Gethsemane did ask the Father for the cup of His coming crucifixion to be assed from Him but nevertheless His will to be done and not His own.
Matthew 26:39 And he went a little farther, and fell on his face, and prayed, saying, O my Father, if it be possible, let this cup pass from me: nevertheless not as I will, but as thou wilt.
When Jesus said He did not come to do His will but the Father's will, He was speaking as Son of man and the aspect of His earthly mission of perfect righteousness----complete unwavering obedience even to the Law that He was born under as Son of man, and for us not for HImself. Of course that was the Father's will but that does not mean that before creation, before His incarnation, it was not also Jesus' will. He came and did what He did, even to the point of death on the cross, willingly.
I understand your point here but what I had shared does not refute nor take away from that truth that the Son did have His own will to pray like that in the Garden of Gethsemane but He did and still does the will of the Father.
