I think the whole story were about FIRST humans, not ONLY ONE humans there. They had 2 boys, yes, but I bet God created more people to live in actuall INFINITE Eden garden. All stuff about Adam and Eve is a shortcut.
A shortcut to tell, that we arent 100% good. That our mind works differently and we go against rules from time to time, as we are only humans, not some overpowered beings. Thats why we have free will and God provided some rules to follow them, to have easier life, yet still let u have choice.
No matter if you believe or not, are christian, muslim, atheist, buddist… The rules are simple. Same goes with “deadly sins” and “commandments”. Be polite, kind, don’t fuel yourself with anger and hate only, love yourself and others, be merciful, dont fall into lust (so there wont me STD, unwanted childrens, the choice between killing the inmocent fetus or not). Like, these are more like guides than rules.