They`re Mirror imágenes of themselves , but tu can say they`re twins . cause twin = 2 . and yeah . fans think of them as twins.
KEI stated in an interview that he specifically did not diseño them as twins, and was told the two are más like mirror imágenes of eachother and diseño them as such por CFM. He dicho since he didnt diseño them at the same time (Rin came first), Len ended up looking a lot like Rin and was mistaken as her twin brother. He did not mean for them to be twins.
EDIT:
Len's voice is not altered in any way. Asami Shimoda was hired because she is able to create both male and female sounding voices. Len is Asami's raw voice without any editing :]
She sings as both Rin and Len in Rin Rin Signal (
link )