Don't ever worry about looking foolish. You will be a bigger fool if you agree to something you don't understand or feel right about, than if you back out now. Many people put engagements on hold, that's really no big deal.
What you wrote about it is very confusing. "Be my wife but not really my wife." Or was it the second guy who said he doesn't want to marry you? If this is how you expressed what is happening, you must be just as confused as I am. Don't be embarrassed to ask for clarification.
And it sounds like he is asking you to be in a relationship with someone you don't even know! WTF!
Listen, poly relationships are no different than mono ones in the respect that they all require clear communication, respect, honesty, caring, affection, commitment, etc. There are just more relationships to manage. Don't think that you have to go along with stuff that doesn't sit well with you or offends you, just because you feel you don't know enough about how poly works. Whatever you do, protect yourself and DO NOT mix your money with his! If I were you, I would put everything on hold until you get clear and understand what the hell and how the hell his cockamamie ideas about a polyandrous tribe are supposed to work out for you both.
The world opens up... when you do.
Oh, oh, can't you see? Love is the drug for me. ~Bryan Ferry
"Love is that condition in which another person's happiness is essential to your own." ~Robert Heinlein