why is 'leanyok' not correct?
Report it, I think leányok is correct.
It's correct, be aware it's oldish/can sound like some literary cliché.
I first encountered this form visiting Leányvár, the girls' fortress of the roman castle Kelemantia east of Komárom / Révkomárom. It's on the Slovak side since 1919.
How about "we are girls and you boys?"
I think English requires a second 'are'
It doesn't require it, but the form without the second 'are' is rather literary in style.