Very good discussion on the legal side of marriage without state paperwork, revealing many issues you may not have considered before. The Survival Podcast, interviewing a woman in a polyamorous family, but one man two women so very similar to the situation of most Christian polygynous families from a legal perspective.
http://www.thesurvivalpodcast.com/stateless-marriage/
Very USA-centric discussion, and US laws are far more complex and statist than many other countries (the "land of the free" rhetoric is pure propaganda so the slaves don't realise they're enslaved), so some parts of it are not relevant in other countries, but this gives a comprehensive list of issues to look into to check the implications in any other jurisdiction.
http://www.thesurvivalpodcast.com/stateless-marriage/
Very USA-centric discussion, and US laws are far more complex and statist than many other countries (the "land of the free" rhetoric is pure propaganda so the slaves don't realise they're enslaved), so some parts of it are not relevant in other countries, but this gives a comprehensive list of issues to look into to check the implications in any other jurisdiction.