Hmm...interesting question. I have seen some folks on here who keep a Kosher kitchen that simply do not allow people to use the kitchen instead of having to ask guests whether they are kosher or not, or only accepting kosher guests. But since the main function of renting an Airbnb is to have a place to sleep, that probably isn't the right approach for this situation. (denying kitchen access would be different than denying sleep access).
I understand that you do not desire any feedback on whether your desire to ban unwed people from sharing a bed is particularly Christian, moral, compatible with Airbnb culture etc.
Therefore, I would just suggest that in your house rules you stipulate that you only rent to unwed persons if they are willing to sleep in separate beds. You should probably define "wed" for your guests, as some people have a common law marriage which does not come with a marriage certificate but stands in court as marriage. (From your description it sounds like you would define such a marriage is co-habitation). You should also consider whether you would consider a valid, state-sanctioned union between two people of the same sex as marriage, as many same-sex couples do have a valid marriage certificate, are legally defined as a married couple, and I must presume that according to your religious background these unions would not count as "holy matrimony" in your eyes, and in this instance you might prefer to stipulate that you do not want these married people to share a bed in your home. You should think about what you would want to do in the instance that people have differing last names, as that is culturally quite common in some places. Also, whether you would require a marriage certificate or if their word that they are married is enough.
You may also care to consider that Airbnb has in the past banned hosts that discriminate, for example a host was removed for denying a room to a guest on the basis of their transgender identity.
