That's an argument most Christians can't win.
How many gods are there in the Universe? How many make up "God"?
We know that the Father is God,
The Son is God, and,
The Holy Spirit is God
It's like asking how many people are in a family? Or, how many people are in a quorum?
God (Elohim being plural) isn't physically ONE God. It can be three gods, five gods, five hundred, five thousand or five million. There's no set limit.
Jesus prayed to the Father concerning the apostles, "...that THEY may be ONE, even as WE are ONE."
This clearly means that in the same way WE are ONE, Father, THEY should be ONE. Does this mean that they should be physically ONE? Not at all. In fact, the apostle John makes it fairly clear that those who become co-heirs with Christ become ONE with God. That means that as children of God, we can become like our Heavenly Father and like Jesus Christ.
It's a doctrine called theosis.
“ I have said, Ye are gods; and all of you are children of the most High. ” (Psalm 82:6)