Are they demanding marriage licenses for it, or are they fine simply cohabitating. If there’s anything that polygamists do well with, it’s living like they are married with people even though they have only one marriage license, if any at all. The state doesn’t care if you cohabitate without marriage, you pay a fine to get a marriage license, and you lose a lot of advantages that you had from being unwed, such as pay less individually when you file taxes as an individual.
And it will even SUBSIDIZE any offspring generated by the endeavor.