"Are you replying to us or to them?"
Translation:Odpowiadasz nam czy im?
If you ask an A/B question, you use 'czy'.
'albo' would suggest that the answer can easily be "Neither A nor B" or "Both A and B". Which is maybe not impossible, but doesn't seem very probable here. So frankly, on the level of being just a learner here, it's better to stick to using 'czy' in questions. You rarely mean something else.