There used to be a video on YouTube (on the official 迪士尼 Channel account) explaining the tricks behind this, but unfortunately it's not up anymore.
Anyway, 鸽子 Cameron has two 女演员 who portray her "doubles" - they are listed as "Liv 2" and "Maddie 2" in the end credits of each episode. We only ever see the backs of them in the episodes, and they're there whenever both Liv and Maddie need to be on screen at the same time. 鸽子 plays the one whose face we see, and one of her doubles stands on screen as the other twin!
When 鸽子 is on screen as both Liv and Maddie, there is a line on set somewhere that the other actors have to make sure they don't cross! The cameramen record one side of the set where she is 表演 as Liv, and the side where she is 表演 as Maddie, separately. Then the editors put both sides together so it looks like there are two 鸽子 Camerons!
Sorry if I haven't explained it very well! If 迪士尼 ever puts that video online again I'll give 你 the link. It's pretty cool!
Anyway, if you're interested in seeing what "Liv 2" and "Maddie 2" look like from the front, I found these pictures here where 你 can see 鸽子 Cameron with them!
Pics of 鸽子 and her doubles:
link I hope this has helped! :)
