Which case is ludzmi in this sentence; intrumental?
Why do we need instrumental?
Check https://www.duolingo.com/comment/16373167 - especially Part 2.
Can a group of women also say Ještemy ludžmi?
Well they can say "Jesteśmy ludźmi"
a band of brothers
(Pendragon is a polish band)
Can we say 'my są ludźmi'?
You could say "My jesteśmy ludźmi".
"Są" is only for 3rd person plural, which is not the case here.