"Do you think about us or them?"
Translation:Myślisz o nas czy o nich?
Mysli pan o nas czy o nich? sounds better. - both sentences are standard Polish but sound like something a (child) student would say to their teacher. O kim Pan myśli, o nas , czy o nich ? sounds more like what would be asked ( Who do you think about, us or them)
No, "nich" has to be used after a preposition and "ich" cannot be used there, so they exclude each other.