It is completely legal for you to say "unfortunately we only allow 1 person per room and no outside guests for more than 2 nights a week."
In addition, because you are living in the home, you can legally discriminate based on gender (but you cannot advertise in that way). In other words, advertise your dwelling as if it were non-owner occupied, but if someone does not fit your criteria (i.e. a married couple wanting to share a room), you can legally discriminate based on gender because you live in the home (see specifics below), but to avoid them being upset, you can make it more about the rules of the property (i.e. one adult per room) rather than it being about gender (i.e. boys only).
Under the federal Fair Housing Act, landlords who live in a property with four or fewer rental units (this would include your situation) are exempt from all but one aspect of the federal law: They may not advertise in a way that indicates a preference for (or against) members of a protected class (race, color, religion, national origin, sex, familial status and disability). And, there is an exception even to the exemption: You may advertise for a lodger of a specific sex (and you don't have to specify your own sex).
Pro-tip: If you reject someone's application or interest in your property, always offer to help someone find another place to live or at the bare minimum, suggest websites for them to check out additional properties. This not only helps them, but makes them way less likely to be upset if they do not fit your criteria for living (i.e. financial requirements and/or gender *if you live there*)
Hope this helps!
