The US in Genesis 1.26-27
Who's the "us" in Genesis 1:26-27? Who was God speaking to?
I'm sure I know of no satisfactory explanation for the "us". It's more a case that some explanations are less likely than others. Some scholars have taken the view that it's a polytheistic version of the creation story that was taken and made part of the Genesis narrative. Of course Genesis 1 is explicitly concerned to expose polytheism , especially Egyptian polytheism that Israel had so recently seen shamed and exposed in the plagues. So it hardly makes sense that someone made use of a polytheistic snippet to write his narrative.
Early Jewish interpretation took it that God was speaking to his heavenly court (compare Job 1:6 and 2:1 and perhaps, Isaiah 6:8), the angelic beings.
I tend to agree with that view and see it as God preparing to create his "masterpiece" and saying to the enthralled angelic watchers as a man might say to his children who were watching him build something (compare Job 38:4-7), "Now, let's put the finishing touch on it."
I've said he says to the angelic watchers but it would probably be more accurate to say that he says it "in the presence" of the heavenly court. It would probably be more that he is speaking to himself. Not in any formal manner! But sort of murmuring to himself, "Now..." This might ease the little difficulty of the "our" image phrase.
Since there is no development of the doctrine of the Holy Spirit or Satan or the resurrection, and such, in the OT I wouldn't expect a development of the plural unity of God, though there are hints of it (compare Psalm 110:1 and Jesus' use of it). So I wouldn't be prepared to rule out the plural unity of the Godhead.