“how do you know some of these gods are not real?”
Because my God crushed them all 2000 years ago!! ;)
Tsk, tsk, the saint you named yourself after would agree with me if I said that you got your dates all wrong.
The God you speak of made clear that there are no other gods beside Him, some 3400 years ago, when He made that His First Commandment and handed it to Moses in addition to nine others.