We had a very similar thread last year that’s probably going to have some of the examples from this thread (including the Ashmores, who I mentioned in that thread):
The contribution I want to make is Enver Gjokaj, a very prominent actor that I first was aware of from his major role in the TV show Dollhouse.
He has an identical twin brother named Demir. In one episode of Dollhouse, his twin brother was a guest star in a dream sequence.
Demir’s only credit in IMDB aside from that guest role was as himself on an episode of the reality show The Legend of Shelby the Swamp Man.
Sadly, one of those twin boys (Sawyer Sweeten) took his own life at the age of 19. 