"Are you people thirsty?"
Translation:क्या आप लोग प्यासे हैं?
क्या आप प्यासे हैं should be valid. English doesn't have a separate plural second person pronoun, so you have to add 'people' for clarity. But in Hindi, 'लोग' is optional. 'आप' by itself can very well mean plural.
I wondered about that--does Hindi ever add लोग to clarify that they mean multiple people and not just a polite "you", or does this sentence seem unnatural to a native speaker?
Both - inclusion and exclusion of "log" - are natural for me. To the best of my knowledge, whether one uses it or not is just up to preference, and somewhat depends on where the person is from.
I think most native (American) English speakers would not say "you people," as it has kind of a weird racial outsider connotation. Depending on the dialect, we're more likely to say "you guys," "you all," "y'all," "all y'all," etc. Or just "you" is also fine if it's clear we're talking to a group.
pyāsā honā has negative connotations. One would rather say, "Kyā āp logoñ kō pyās lagī hai?"