All of the Fairies from this era are played by by the Peanut sisters, Emi & Yumi Ito. However, in the 1966 movie, Godzilla vs the Sea Monster, they are played by different actresses. In that film the Fairies are played by, Yuko & Yoko Okada, the Pair Bambi. The Fairies in all of the movies, from the Showa era, are called, Shobijin. They all have psychic abilities, including telepathy, & in Mothra vs Godzilla, they demonstrate teleportation while escaping from Torahata & Kumayama. Lastly, they can understand monster roars.
Mothra's Fairies from the first movie of the Heisei era, Godzilla & Mothra 1992, are actually the Earth's Cosmos, Keiko Imamura & Sayaka Osawa. This makes them different from the Shobijin because they speak for Mothra, Battra, & the Earth itself. They know where Battra is at all times, know when he is awaken, & feel concerned for him when he gets hurt. Also, if the Earth is in pain, they will know because they can talk to the Earth. But, they're pretty much the same because of their psychic abilities, & being a foot tall. Then, there are the Elias from Rebirth of Mothra 1, 2, & 3, from 1996-1998. Moll, one of the good Elias, is played by the same actress through the entire Rebirth trilogy, Megumi Kobayashi. However, Lora, also one of the good Elias, is not played by the same actress through the whole trilogy. She is played by, Sayaka Yamaguchi, for the first two movies, but is replaced with, Misato Tate, in the third film. There actually is a third sister, named Belvera, played by Aki Hano in all three movies. She is the evil sister, who wants nothing but humans to die. But, anyway, all the Elias, including Belvera, have cool powers, for example: Telekinesis, & the ability to, I guess, defy gravity, for short whiles.
In the first movie of the Millenium era with Mothra the Fairies aren't really Fairies, they're just normal people. The reason I call them Fairies is because in, GMK from 2001, a pair of twins looked at Mothra as she flew by, while everyone else ran away. The next two movies Mothra did have actual Fairies with her. First, was Godzilla Tokyo SOS, 2003, where they were the Shobijin. The Shobijin were played by Masami Nagasawa & Chihiro Otsuka, who both did fantastic jobs. Lastly, in 2004's Godzilla Final Wars, Masami & Chihiro, reprized their roles as the Shobijin.