Roomate is 'sibling', and Landlady is 'Mother'. I thought this was obvious. They are in fact taboo, obviously, but most mediums by which the artists make money frown heavily upon this, though that is a mostly American perspective.
As an example, ask someone French, Italian, Spanish, Greek, Japanese, Chinese, Mongolian, Russian, Indian, or German if an Aunt marrying her Nephew is legal where they come from. Hint: it is completely legal.