Sorry you don't believe in marriage. Unfortunately there's more and more people like you, to the determent of society in my opinion.
As for your Biblical questions....I've taught weekly in depth Bible classes for more then 20 years and readily admit that I've only scratched the surface of what the Bible has to teach mankind. I don't claim to be any kind of Biblical expert.
Since the Biblical account says God "gave" Eve to Adam I guess you can say that He "married" them with His command to "be fruitful and multiply". As for the Patriarchs, yes, most had plural marriages in accordance with their laws and customs of the time and God blessed those unions. Was there a marriage "ceremony". Don't know but I expect it was formalized in some way.
That said... nowhere in the Bible is fornication identified as anything other than sin.
This is why I rarely post. Very tiresome unless you automatically agree with "the crowd". That's my last post on the subject so don't expect any further reply.
Could the Bible teach us that the way we view marriage isn't how God views it? You say yourself that you have only scratched the surface. Could God be saying that Bristol and Levi are married in his eyes? I know you wont respond but you could consider what I am saying.