My brother, for example, is devoted to a materialism/scientism that in no way allows for the existence of anything that is presently mysterious to science
That "in no way allows for the existence of anything that is presently mysterious to science" would certainly be a problem, given the practical reality that there are clearly many things that are presently mysterious to science.
A lot of Epicurean philosophy is devoted to exploring a proper approach to dealing with things that are currently unknown.
You obviously have a lot going on in your thinking and it's going to take time to deal with so many different aspects of things. Once you have time for enough reading I think you'll see why I recommend the DeWitt book so highly. He'll give you a good grounding on Epicurus without a lot of extraneous comparisons to other philosophies (other than the Platonic viewpoints to which Epicurus was reacting). That will be the quickest way to understand Epicurus on his own terms without filtering him too strongly through other paradigms and the sidetracks which that would entail. Once you do that you'll then be in a great position to circle back and decide how he stacks up against the eastern analysis.