Hi Sana,
Welcome to the forum
Before you can hope to teach anybody else truth you must first get it firmly understood in your own mind. And as you indicated you do need Scripture to give you the confidence in what you believe.
" If God has already subjected everything to Jesus Christ and , YHWH is Jesus Christ, after he resurrected why he is sitting on the right hand side of the Father , when already God has subjected everything to him?"
It is true that God the Father has subjected all things to Jesus Christ, and the Verse that Extol provided makes it clear that does not include the Father.
1Co 15:27 For—He (the Father) put, all things, in subjection under His (Jesus Christ) feet. But, whensoever it shall be said—all things are in subjection!—it is evident that it means,—Except Him (the Father) who did put into subjection, unto Him (Jesus Christ), the all things— (Rotherham)
Heb 1:1 In many and various ways God spoke of old to our fathers by the prophets;
v. 2 but in these last days He has spoken to us by a Son, whom He appointed the heir of all things, through whom also He created the world.
v. 3 He reflects the glory of God and bears the very stamp of His nature, upholding the universe by His word of power. When He had made purification for sins, He sat down at the right hand of the Majesty on high,
It is God the Father who is the power and source of all that Christ has. Everything comes from the Father and for this creation it is being accomplished by Jesus Christ.
2Peter 1:17 For He received from God the Father honor and glory when such a voice came to Him from the Excellent Glory: "This is My beloved Son, in whom I am well pleased."
John 5:19 Then Jesus answered and said to them, "Most assuredly, I say to you, the Son can do nothing of Himself, but what He sees the Father do; for whatever He does, the Son also does in like manner.
John 5:30 I can of Myself do nothing. As I hear, I judge; and My judgment is righteous, because I do not seek My own will but the will of the Father who sent Me.
So Jesus Christ is the God of the creation, that is the purpose of Him. It is through the Son that the Father works all things that are being done in this physical world.
1Cor 8:6 nevertheless for us there is one God, the Father, out of Whom all is, and we for Him, and one Lord, Jesus Christ, through Whom all is, and we through Him." (CLV)
Rom 11:36 For of Him (Jesus Christ) and through Him (Jesus Christ) and to Him (Jesus Christ) are all things, to whom be glory forever. Amen.
Hope this helps. Study the Scriptures and get these truths firmly fixed in your mind and you will not be confused or upset by the contrary statements that others make.
mercy, peace and love
Kat