Genesis Chapter 4 begins with the words VeHa'Adam yada` 'et Chavvah 'ishto, vatahar vateled ben ("Adam had previously known Eve his wife and she conceived and brought forth a son"). This means that the conception (and that of Abel which follows) had already occurred in the Garden before the expulsion. If the conception and birth had been after the expulsion it would have used the "vav consecutive": Vayeda` Ha'Adam 'et Chavvah 'ishto vatahar vateled ben.
The number of children (Cain born with a twin sister and Abel born with two "triplet sisters") is part of the Oral Torah handed down from Sinai. As a Protestant you don't accept the Oral Torah and I doubt anything I say could change your mind. Unfortunately for you, however, the Written Torah (which is all you accept) consists of nothing but consonants--there are no vowels and no punctuation. If the Oral Torah is "the doctrine and commandments of men," then the Written Torah is unreadable, since the vowels and punctuation which are necessary to understand it are the work of fallible men. Also unfortunately for you, the authentic Written Torah text has been preserved for 3300 years because of the Oral Torah's rules for writing Torah Scrolls, without which the first copy could not have been made and the text would have disappeared from history, G-d forbid.
I realize you will not agree with me. I hope you will not be angry with me for believing differently than you.
Well; since I've never heard of your traditions and oral stories; any DISagreement would be because of my ignorance.
I hope you will not be angry with me for believing differently than you.
I do not get angry because of that.
I would be angry with my past self if that were the case.