"We swim, whereas you fly."
Translation:Mi úszunk, ti pedig repültök.
No, it's not a correct translation for this sentence. In sentences like this "pedig", when used as "whereas", always needs an explicit subject in front of it. I think.
(There is another meaning of "pedig" as "although", which can be used without an explicit subject or with a subject after it, so "úszúnk, pedig [Önök] repülnek" would mean "we are swimming although you are flying".)