The speaker is clearly Isaiah himself.
Many times in the book of Isaiah God speaks though Isaiah then Isaiah speaks as well. The prophet was sent by God, given the power of the Holy Spirit to preach repentance to Israel.
No where in that chapter is the Trinity found. The Trinity is a pagan theology that came from that abomination called the council of Nicea. It has corrupted the true meaning of the Father and his son Jesus.
As to your second quote. The word "Word" is from the Greek Logos.
It means the plan of God. Thus John is telling his readers that the plan of God was with God from the beginning. Thus he goes on and says that the word/logos/plan of salvation for mankind was made flesh with the birth of Jesus.
In addition calling the plan of God, the logos "him" is like calling a table "he".It makes no sense. Thus the true translation of your verses should read
2 It was in the beginning with God. 3 All things came into being through it, and apart from it nothing came into being that has come into being. 4 In it was life, and the life was the Light of men. 5 The Light shines in the darkness, and the darkness did not comprehend it.
Um, no. But thank you for the conversation. You are free to believe as you will... God gave us free will. I will not change your mind but I pray the Spirit will in His own time.
May God bless you.