Everybody in Toobworld has a twin; that's a given. Most are related by blood, such as actual identical twins, or maybe half-siblings. Sometimes the relationship is a little farther out, like identical cousins who walk alike and talk alike. Or maybe there's a generational difference - sometimes parents look exactly like their children (Felix Unger and his dad, Morgan O'Rourke and his father). Identical twins can also be caused by plastic surgery, by magic, or be due to android duplication and alien shapeshifters.
Most rare are the identical twins related to each other not by blood, but by marriage. And in my :ahem!: sciolistic research yesterday into the identity of the first Mrs. Sam Malone, I discovered that Carlie Kirkland of 'Banacek' (1972-74) may well have been the exact double to Virginia Kirkland, seen in the "Fatal Overture" episode of 'Barnaby Jones' in 1979. But in my theory, they obviously can't be sisters or cousins, but instead perhaps they were sisters-in-law.
Here's a description of that episode:
"Betty witnesses the quarrel of a neighbor with two women. On the next day one of them is dead and the man, Peter Kirkland, asks Betty to investigate the apparent suicide. He fears his jealous, unbalanced wife Virginia might have committed a crime."
It's my supposition that Peter Kirkland and Carlie Kirkland were brother and sister, but that Carlie lived in Boston while Peter lived in the City of Angels. It's no wonder Peter's wife Virginia was mentally unbalanced.... Ladies, how would you feel if you found out that your husband married you because you were the spitting image of his sister?
Let's crank up that Eww Dial to 11, shall we?