Polygamy in the Bible

[Dora]

So how would you counsel a couple who came to you for marriage guidance and they announced that they were engaging in polyamorous relations with an "extra" and were practicing fidelity between all parties involved and that they would get married except that it is against the law??? Would you condone the behavior or would you counsel them to terminate the relationship with the "extra" not on the grounds that it is conduct unbecoming a Christian, but because it is against the law??? or would you say go on with your bad selves???