Some modalists assume that simply because the term "Father" is applied to Jesus in Isaiah 9:6 (9:5) that this means Jesus is God the Father. This is not the case at all. "Eternal Father" (Avi Ad in Hebrew) simply is a term of authority here. The whole subject of Isaiah 9:6 (5) and the subsequent verse Isaiah 9:7(6) is about authority. Making references to the "government" "counselor" "El" (which can mean God, judge, mighty), "Father" and "Prince."
The term "father" is used elsewhere in Isaiah 22:21 where it says about Eliakim
I will commit thy government into his hand; and he shall be a father to the inhabitants of Jerusalem, and to the house of Judah.
We see the term "father" here is just an authority figure.
Likewise, when Joseph was made an advisor to Pharoah and given authority he says of himself that he was a "father to Pharoah" (Genesis 45:8)