While I understand the concern you have over cooperation in sin I do not think the situations you are speaking of qualifies as that at all. Shelter is a basic human right. It is wrong to deny shelter to others simply because they are sinners. If the people in question are in fact planning on sinning against chastity they will do so wherever they end up staying, are we supposed to kick them out onto the street just because we suspect (even if we have strong suspicions) that they sin against chastity? All you are doing is helping to provide a basic human right, shelter, to others. That is not sinful. Now, if you were congratulating same-sex couples on their relationship, or encouraging it that would be one thing, but if all you are doing is providing them shelter then I honestly do not see how that could be an issue.