There have been hundreds of live action dc heroes and villans played by mutiple actors in tv and movies like some old serials, The 1950s George Reeves "Adventures of Superman,"1966"s Batman 1970"s Wonder Woman Superman '78 (including Supergirl '84) two "Swamp Things," a "Superboy" TV series, and Batman '89-'97 (Burton and Schumacher) The 1990"s Flash "Lois & Clark." Smallville" 2001-11, The Dark knight Trilogy The Arrowverse Arrow, Flash, Legends, Constantine, Supergirl and Earth 2(Jay Garrick et al.) The Gotham series on Fox Man of Steel/DC Cinematic U , Green Lantern 2011 so Are all the Dc live action heroes from movies and TV universes exist in the same universe but as different earths in the multitverse
First, a couple definitions...
In a standard universe, there is only 1 ("uni-") of each individual thing. One Earth, one Milky Way, one Superman, one Flash, etc. Even when someone gets cloned, there's still the original and clone A, clone B, clone C...
A multiverse ("multi-" = many) is the collection of all the connected universes. The multiverse contains universes--not the other way around. So there's an Earth-1 in Universe-1, an Earth-2 in Universe-2, an Earth-3 in Universe-3, and so on. Think of a bag of inflated balloons. Each balloon is a universe, and the bag holding the ballons is the multiverse.
Earth-1 is sometimes referred to as "Earth-Prime" with its universe being the "main" universe. In our human-centric stories, Earth/Earth-Prime is often considered the dramatic focal point of the universe and often the multiverse as well.
Sometimes the differences are minor (the sky is pink instead of blue), and sometimes the differences are major (the Nazis win WW2). There is both a Marvel and a DC multiverse, as well as other multiverses not belonging to either (citation needed).
Now to your answer...
In the movies and TV, pretty much each time a DC character is portrayed by a different actor, you're seeing a different universe--but they're all part of the same DC multiverse. In other words, there's the George Reeves universe, the Christopher Reeve universe, the Tom Welling universe, the Dean Cain universe... But each of those universes is part of the DC Multiverse.
Occasionally an actor in a series is simply replaced with another actor (Rachel Dawes in the Nolan Batman movies, Rhodey in Iron Man), but the rest of the cast remains the same and the story stays in the same universe.
And here's another person asking basically the same thing.