wypiłyśmy is a perfective aspect, correct? If so, then there is no reason for the English translation to be in the present perfect tense. It should just be simple past tense "We drank orange juice."
Piłyśmy, if there is such an imperfective aspect, would more properly translate as "we have drunk orange juice [in the past, whenever, at no particular time]."
I think piłyśmy should be translated as we were drinking, as this aspect suggest the drinking wasn't finished (or the end doesn't matter) - as in We were drinking when something happened - definitly piłyśmy should be used here.
piłyśmy = we were drinking (as in, this is what we were doing); wypiłyśmy = we drank ( as in, we done drank, drank it all up, finished drinking the orange juice) ? Technically, I think the translation "we have drunk (the) orange juice" is (grammatically) correct, in this context. Except no one says that in real life.
I think we might say "we drank the orange juice" to indicate the perfective (that you finished drinking it) and rather "we drank orange juice" (without adding 'the') to indicate that that is an activity you were doing, without necessarily finishing it (niedokonany/ imperfective)