As a disclaimer I should say that I unequivocally reject the Genesis account with regard to its historical reliability. It's a made up myth designed to account for the origin of mankind, the unjustice and iniquity of the world, as well as our own mortality, that ever present, unvanquishable enemy. It's also an attempt to explain other more seeminly mundane things in comparison, such as why women suffer so much during labor, and why snakes don't have legs.
Yet, when attempting to interpret Hebrew scripture, I prefer to allow the text to speak for itself. I begin with the assumption that the text means what it says. Genesis is presented as a historical fact, complete with detailed geneologies. The idea that it's all allegorical is in my opinion nothing more than a pitiful attempt by apologists to dismiss the most easily verifiable historical inaccuracies of the bible, while still maintaining a basis for their belief in Jesus and all that jazz.
When Elohim (Gods or "THE God" (Hebrew used a plural to sometimes show the excellency or uncomparable nature of someone or something, much like we use the royal "We"). Others will argue that "Elohim" refers to a pantheon of gods, in the pre-monotheistic past of Judaism. I'm not sure who to believe on that one though.
Either way, I hardly believe this constitutes support for the Trinity doctrine. In the Hebrew Scriptures (Old Testament), it would appear that the Israelites had no concept of a person in heaven such as Jesus Christ. There is never any reference or even an inkling of an indication that they believed in or knew of a spirit person existing in heaven as the "only-begotten" Son of God. They did however, believe in the existence of myriads and myriads of Angels. They called them Angels, cherubs, seraphim, "sons of God", "sons of the Most High", "glorious ones", "morning stars", etc.
So, within the religious context, it is clear that the Hebrews never believed God to be all by himself up there in heaven. They thought of him as being among millions of other spirit persons. Hence, when he is obviously speaking to someone in heaven, the "US" would then be a reference to the angels. "Us" can be as many as two persons, or as much as a billion persons or infinitely many people. It certainly doesn't necesitate that "us" only refers to God and Jesus, or to God and two other members of a mythical Godhead.
When it talks about "them becoming like us, knowing good and bad"... I again allow the text to speak for itself. People, including JWs try to dismiss this quotation as figurative. They claim that the fruit offered no supernatural powers, but merely that the act of eating the fruit symbolized a decision made by Adam and Eve to alienate themselves from God. They espouse this view only to make the text conform to the more pragmatic mind of a modern reader. When Genesis was written, it was read and passed along by people who believed the earth was the center of the universe, that there was a metal dome encapsulating the planet, that the sun, moon, and stars were created after the earth, and that snakes could talk. These people believed in mythical, mystical, supernatural things such as sticks turning into snakes, women being turned into pillars of salt, talking donkeys, etc. In the case of the tree of the knowledge of good and bad, it would seem to be more than just a symbol. The text says that immediately after eating the fruit, their eyes were opened. It brought about a change in their pysche, in their self-awareness. Before eating of the tree, they were essentially like innocent children. They were not capable of evil, and they couldn't think independently of God. If God said something was bad, they like robots, would agree and feel that thing was bad also. They could not determine for themselves what was bad. They were entirely dependent on what God told them was good or bad.
Then they eat the fruit, and suddenly they're free thinking individuals, with their own tastes, and opinions on what was kosher or not. Poof! Just like that. The downside is that they no longer have God's super powerful spirit artificially sustaining their life indefinitely. That gets immediately cut off, and their biological, organic, fleshly body is allowed to undergo the natural degenerative aging process that all living, biological things experience. They're now doomed to die.
Up until this point, one might still try to claim that the eating of the fruit itself was not the cause of this change, but that the fruit tree was only a symbol for a more profound spiritual transformation. Yet, consider this. If eating the fruit meant nothing in itself, then why the rush by God to seal off access to the Tree of Life? Why was he so concerned about the tree if the tree didn't offer any powers of immorality, and was instead just a symbol? The answer is that according to the story, it did! If Adam and Eve had got their hands on the Tree of Life, they would've been both free of God, and immortal! That's something God would not allow. Their defiance could not go unpunished, and they had to be made an example of.
That's why I think the author(s) of Genesis intended for the fruit of both trees to be understood as literally confering powers upon man, rather than just symbols. That's what jumps out at you from reading the text.