I will have to study and see where the name Yah comes from. I know as a christian we believe there is only one God, and this one God is in three persons.
God the Father
God the Son (Jesus Christ)
God the Holy Spirit
The persons are distinct yet they are one.
The Father is God and is the first person of the trinity.
The Son is God and the secound person of the trinity.
The Holy Spirit is God and is the third person of the trinity.