The demons knew who Jesus was (not YHWH). There's a clue in what the demon said - "What do You want with us,
Jesus of Nazareth?".
Who do you think "the Holy One of God" was? Hint, Luke 1:35 (WEB):
The angel answered her, “The Holy Spirit will come on you, and the power of the Most High will overshadow you. Therefore also the holy one who is born from you will be called the Son of God.
Yep, it's referring to Jesus. The demons knew that Jesus was the holy one of God, the Son of God. They did not think that he was God (YHWH).
You totally misunderstand that verse. See previous post in this thread for an explanation.
How is that our Father declaring that Jesus is YHWH? Peter said that the lame man was healed in the name of Jesus, God's anointed (the Messiah), and that God had raised Jesus from the dead. God YHWH cannot die, therefore clearly Jesus could not have been YHWH, because Jesus had died. God has determined that only through His Son Jesus can we be saved:
Colossians 3:17
Whatever you do, in word or in deed, do all in the name of the Lord Jesus, giving thanks to God the Father, through him.
1 John 3:23
This is his commandment, that we should believe in the name of his Son, Jesus Christ, and love one another, even as he commanded.
Php 2:9-11
(9) Therefore God also highly exalted him, and gave to him the name which is above every name;
(10) that at the name of Jesus every knee should bow, of those in heaven, those on earth, and those under the earth,
(11) and that every tongue should confess that Jesus Christ is Lord, to the glory of God the Father.