I would like to offer a very different perspective, if I may.
Originally Posted by g71
. . . I have been the second wife in a relationship for almost 10 years.
. . .
Im my current situation wife one is legally married and reaps all the benefits therein.
For a lot of reasons, including that I don't seem to be worthy of a legal marriage even for a little while. I have decided that at 40 I am going to start over again. This time in a position of being "wife one", primary what-have-you.
It sounds to me like what you're looking for is a new situation to cure problems in your current situation. That is a lot of baggage to load onto a new relationship and not many would be able to stand the strain.
If you feel you are not being fairly treated with respect to taxes, insurance, etc. you are completely justified to insist that your partners work with you to redress that unfairness. There is always a way to find a fair balance; sometimes "equal" is an unreasonable expectation, but fair is always possible.
Unfortunately, social respectability is not something that can be conferred from within your triad. Those are choices every single member of our society makes, and somehow some weird form of consensus is reached, based on all sorts of conscious and unconscious influences and enculturations. But you probably knew that going into the relationship, and decided it didn't matter, or not enough to deter you from going ahead. But it matters to you now. Fair enough; people change. Have you done everything you can to address these issues with your partners? For instance, there are countries where plural marriage is legal. Even within the Western world, there are areas where alternative lifestyles like poly are much more openly tolerated, even if they aren't recognized legally. Have y'all looked seriously at relocating?
Good luck to you, whatever you decide to do. I hope you find what you're looking for.