The correct answer is: Neither you nor your sister should talk to them.
The verb “talk” is used to express the action of speaking to someone. In this sentence, the subject is “neither you nor your sister.” The verb “talk” is conjugated in the simple present tense, which is used to express habitual or repeated actions. The negative particle “should not” is used to express a prohibition.
The other options are incorrect because they do not agree with the subject of the sentence or the tense of the verb. Option A, “talks,” is in the simple present tense, but the subject is plural. Option B, “talked,” is in the simple past tense, but the sentence expresses a prohibition. Option C, “talking,” is the present participle of the verb “talk,” but it cannot be used as the main verb of a sentence.
In conclusion, the correct answer is: Neither you nor your sister should talk to them.