Isabella,
Long ago for reasons that are probably very different than you suppose, I came to the understanding that the 66 books of the Old and New Testament, as we have them, are unvarnished truth. Also, I am "classic" in my understanding of truth, and not a believer in Hegelian synthesis or the dialectic. Thus the statement "my truth" or "your truth" has no meaning. "Your opinion" and "My opinion" do have meaning.
In classic logic there "givens" and conclusions that can be drawn from those givens.
One of the "givens" here is very simple and related to the word "Biblical."
The Bible is truth, that's why we are polygynous or "plural" in our descriptions of marriage practices. That's the "Family" part.
Realizing of course that the emphasis is always on "Family" when it comes to being Biblical, we are, nonetheless, "Biblical." We would simply be less liberated thinkers if we weren't Biblical, choosing as our "Style Statement" a nostalgic but not necessarily realistic or true view of marriage and family. It would be like a Civil War Re-enactors group or a Medieval club. Quaint.
So, once again, trying to get you to be accepting of MY view, as I am in fact accepting of YOURS, here's the deal:
From a Biblical Truth perspective (right or wrong though it may be in YOUR view), Cain married a direct descendant of his mother Eve. This is bolstered in both Old and New Testament writings. There's no allowance large enough to drive another wife through other than one of Eve's direct descendants, someone dependent entirely on Adam and Eve for their gene map. The MOST LIKELY candidate is his sister, given the time frames involved and the mess with Abel, murder and having to get out of Dodge (so to speak) . It could be by some possible but contortive circumstance, his own daughter, but still a direct lineal descendant of Eve and Adam.
Your view is admittedly hard to decipher. So far you've allowed for the possibility that it's all true (as scripture tells it) but you reject it. It's possible you see it as quaint and interesting, but simply not true. You also may have a Hegelian view of truth and various "truths" (true for me, true for you, not true for both of us, etc, etc.)
Scripture is classic in it's approach to truth. If A is true, and B is not possible with A being true, then B is not true. We don't work toward a "blending" of ideas to "Find a New Truth."
You need to pick an identity for your point of view, a starting point, and express it. Then we can better understand "where you're coming from" and believe me, unless it's the Satanist's point of view that WE as Christians HOLD to the truth, but that YOU as a Satanist fight against it, I'll have respect for that point of view, and you too. If it's the Satanists point of view, I'll respect your honesty.
As for the great many others that disagree, I don't care. I'm not bound by numbers and this too is a classic error of logic known as "argumentum ad populum." As to their level of expertise and education, these too have fancy Latin names regarding errors in logic. As for me, this is where I am "coming from:"
Oh how I love your law! It is my meditation all the day.
Your commandment makes me wiser than my enemies,
for it is ever with me.
I have more understanding than all my teachers,
for your testimonies are my meditation.
I understand more than the aged,
for I keep your precepts.
I hold back my feet from every evil way,
in order to keep your word.
I do not turn aside from your rules,
for you have taught me.
How sweet are your words to my taste,
sweeter than honey to my mouth!
Through your precepts I get understanding;
therefore I hate every false way."