"A light-year is the distance light travels in one year. How far is that? Multiply the number of seconds in one year by the number of miles or kilometers that light travels in one second, and there you have it: one light-year. It's about 5.88 trillion miles (9.5 trillion km)." Source here.
What Are the 2 Earth-like doppelgangers orbiting?
Teegarden’s Star, an M-type red dwarf, toward the Aries Constellation.
How Do We Know Planet B and Planet C are Earth-like at all?
After scientists discovered over 4,000 exoplanets, their research shifted from discovering numbers of said found planets to their characteristics and if they are inhabitable: Two characteristics (among many) that place a planet in a "habitable zone" are detected by its velocity:
A velocity shows scientists if a planet is in "wobble" mode from being acted upon by gravitational forces causing it to orbit a greater center mass, and also if the size of orbiting earth-like planet is of a low mass.
A third characteristic fulcrums upon if the found planet is within the "Goldilocks Zone" wherein it is not too hot or too cold for water to exist in a liquid state (due to the distance at which it is orbiting a larger red dwarf or center gravity).