The sci-fi juvenile novel “Time for the Stars” by Robert A. Heinlein postulated that twins could use psychic powers to communicate simultaneously if one traveled in a ship at light speed while the other stayed on Earth. Interesting idea.
Actually, while they were traveling, beyond a certain relative velocity they could not communicate due to time dilation slowing down the one on the ship too much, but when they slowed down to check out a planet they could sometimes reestablish communication. The benefit of the twin telepathy was that it was instantaneous rather than limited to light speed, so they could communicate without long delays.