Monarchs and viceroys belong to the same?

The same family (Nymphalidae, which contains most black and reddish butterflies). There they split; they belong to different geni (monarch: Danaus, viceroy: Limenitis). Thereby they are also different species, of course. They grew to look like eachother because both are poisonous, and they can maximize that profit by looking alike - if a bird eats either of them, it will avoid the other from then on, too.