You have JUST been asked to consider a mono-poly arrangement
less than a year ago and are not clear on all of that yet.
I think you would both benefit from figuring that out first.
What sort of open model
are you after?
Have you done enough reading?
Have a plan for coping with jealousy
and poly hell?
You don't have that sorted yet and NOW he also asked you to consider
marriage to him? And that offer is just as vague as his polyshipping proposal? What's the engagement supposed to serve? You being exclusive to him while he continues to see others? Is that something you want? You do not want to date others?
If he's proposing marriage, you are still NOT MARRIED. That's called the ENGAGEMENT period where you continue to talk and map out the future plan together. If his offer for building a future together sounds like flaky for you (and it does!) -- don't agree to anything life altering. Do NOT get legally wed. Have a nice long engagement. For years even.
Better a SUCCESSFUL long engagement where you examine your compatibility and come to find you are not compatible and end the engagement time without a wedding than a rushed
engagement leading to an unhealthy incompatible marriage.
Keep your own finances separate for sure.
So, that's the background info. What I'm wondering is if poly families do that at all, just don't marry anyone in the group, I mean. How do big poly groups handle the common-law rule, handle the law?
I am legally wed to my spouse. We expect genetic monogamy. We are not having children with other people. Those are our agreements. ( I think you are just asking about marriage and custody laws and not asking also about joint debts/assets/properties, right? That could be a novel!)
Any other players would have to be ok with that. Anyone wanting babies or legal marriage -- ain't getting it here. It doesn't mean I love them "less" -- it means at my age I am done making babies. I don't want any more. And since it is not legal here to have more than one spouse, I already have the spouse I have? I'm not divorcing him to marry another. Current limit of the law.
Again -- that's all stuff you sort out in the dating time to see if you and dating partner are compatible or not. Date for a while. That is what dating is FOR. Get to know the person.
What's the rush toward marriage and greater committments made too soon?
You could be more assertive in co-creating the plan. And if he's not taking your wants, needs, and limits on board? He's just into what cookies HE gets? Could drop him and seek better partner -- one that has concern for YOU too. Not just himself.
It sounds weird to me too. Be careful.