Correct past tense...The prisoners have drank or drunk from the same cup?

The correct past tense is "drunk".

The verb "drink" is an irregular verb, and its past tense is "drank". The past participle of "drink" is also "drunk".

In this sentence, the prisoners are talking about an action that happened in the past, so we need to use the past tense of the verb. Therefore, the correct past tense is "drunk".