While I am no expert on Hindi, and am in the process of learning myself, I think I can answer your question. "What are you drinking" is not correct in this case because of the tense. Hindi handles the present continuous tense differently. For example: I drink - मैं पीता हूँ I eat - मैं खाता हूँ
I am drinking - मैं पी रहा हूं I am eating - मैं खा रहा हूं
I have linked to another discussion that goes into greater detail on this subject. https://forum.duolingo.com/comment/28223424
Yes, you are correct. In fact Hindi has the following four present tenses What do you drink (Present) What are you drinking (Present continuous) What have you drunk. (Present perfect) What have you been drinking (Present perfect continuous)
Is this asking what they are already drinking or what is it that they want to drink?
What are you drinking and What you WANT to drink are two different sentences. What do you want o drink would be ...Tum kya peena chaHte ho. To WANT is chaHna.
There is no word for ALL in the original sentence. Therefore by inserting ALL you will be not true to the translation.
I put "what do y'all drink?" since Tum can mean you plural. In the Spanish course it accepts y'all as the plural you, but I suppose not in Hindi.
So is the ते suffix used when the gender of the subject is not specified? And I suppose whether तुम is referring to 'you' or 'you all' (plural) is taken from the context.
In general ते would be used mostly for the masculine and you are correct that it is both for the singular and plural. peetee would be be used for the feminine and in both singular and plural.
saying "what are you drinking" counts as incorrect; is this something to do with tense or just an error on the course's part?
What do you drink (Present indefinite).... is different than ....what are you drinking. (Present continuous). In fact there are two more tenses in this category. What have you drunk (Present perfect) What have you been drinking (Present perfect continuous)
The progressive form is a form communly used in english. It is not the case in Hindi as in French. In Hindi, there is a special rule for the progressive form.