They`re Mirror تصاویر of themselves , but آپ can say they`re twins . cause twin = 2 . and yeah . شائقین think of them as twins.
KEI stated in an interview that he specifically did not design them as twins, and was told the two are مزید like mirror تصاویر of eachother and design them as such سے طرف کی CFM. He کہا since he didnt design 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 )