DEAR MISS MANNERS: We are empty-nesters who always seem to have a guest stopping by for a night. I love having guests. What I don’t love is stripping and making the beds! Do I need to provide each guest with a new set of sheets? Is it horribly rude and unsanitary to have two subsequent guests use the same set of sheets? Guests are sometimes cousins, if that makes a difference. GENTLE READER: Are you asking if being cousins makes your guests less likely to think “Ew!” when they open the bed to used sheets? Miss Manners doubts that. But being cousins does make a difference in that you are probab…