"We are sitting on the chair."
Translation:हम कुर्सी पर बैठे हैं ।
To give you the rough idea, 'बैठना' is the action of bring your butt down to the chair. So, as another user said somewhere, बैठ रहे हैं would entail very slowly lowering yourself down in slow-motion. बैठे here implies that the action is completed, and the person is now on the chair. The same goes for standing (खड़ा).
Ultimately it is just a quirk of Hindi, and you should just remember these two don't take continuous form (outside of a few rare exceptions).
What a brilliant explanation. It gave a me a good laugh, thank you.
Just to be sure: "we" are sitting on the same "chair"? I feel bit dumb to ask, but it feels a bit awkward for two to share one chair, but I guess it must be true, otherwise हम कुर्सियों पर बैठे हैं, right?