Your rules and regulations should state than any person residing on community property in excess of 15 days in a 60 day period shall be required to apply for occupancy, shall abide by any application procedure required of incoming residents, and shall vacate community property within three days of demand, if such resident either fails to apply for occupancy or applies for occupancy and is denied.
Remember that the person applying for occupancy is in addition to the tenant already on the premises so the financial strength of such person may not be as integral as the financial strength of your primary tenant provided that it is clear (and in writing) that the additional person is only approved as an “occupant” and not as the primary tenant and that in the event the primary tenant vacates, or is evicted, the occupant must also vacate.
“Married” or “unmarried” persons are not a protected class under state and federal housing discrimination laws. There is no express prohibition against requiring people living together to be married, however a community owner should carefully consider whether such a prohibition makes sense. If the “married” or “unmarried” person is also a protected class, the “married” policy is subject to a claim of discrimination on the basis of the protected class. (i.e. race, religion, families with children.)