"Cook them a tea."
Translation:Koch ihnen einen Tee.
could someone tell me whetehr it is as common to 'jdm Tee kochen' as to 'jdm Tee machen'? since in english, unless it is done in a rather peculiar method, one usual 'makes' someone tea / coffee...
In German, boiling water is cooking it, and a kettle is called a Wasserkocher. It's just a German peculiarity. You would make something like salad, which dies not involve cooking it.
The Imperative in German: http://www.dartmouth.edu/~german/Grammatik/Imperative/Imperativ.html
can "koch" be a verb? if it's a verb, should it be "kochen" to ask someone to do something?
That is correct, it should work. If it isn't accepted next time you see it, just report it.