Question 1 mis sobrinos / tener / estudiar / mucho
Answer 1: Mis sobrinos tienen que estudiar mucho.
Explanation: The subject in this sentence is "Mis sobrinos", that is a third-person in the plural, so the verb must be conjugated in this form. Ellos tienen.
My nephews have to study hard.
Question 2 ustedes / venir / México / ¿verdad?
Answer 2: Ustedes vienen de México. ¿Verdad?
Explanation: The subject in this sentence is "Ustedes", that is a formal second-person in the plural, so the verb must be conjugated in this form. Ustedes vienen.
You come from Mexico, right?
Question 3 yo / creer que / tú / no / tener razón
Answer 3: Yo creo que tú no tienes razón.
Explanation: The subject in this sentence is "Yo", that is a first-person in the singular, so the verb must be conjugated in this form. Yo creo.
I think you are not right.
Question 4 el señor Alejo / tener / noventa años
Answer 4: El señor Alejo tiene noventa años.
Explanation: The subject in this sentence is "El señor Alejo", that is a third-person in the singular, so the verb must be conjugated in this form. El tiene. Mr. Alejo is ninety years old.
Question 5 tú / venir / el laboratorio / los viernes
Answer 5: Tú vienes al laboratorio los viernes.
Explanation: The subject in this sentence is "Tú", that is a second-person in the singular, so the verb must be conjugated in this form. Tú vienes.
You come to the lab on Fridays.
Question 6 Tamara y yo / tener / hambre y sed
Answer 6: Tamara y yo tenemos hambre y sed.
Explanation: The subject in this sentence is "Tamara y yo", that is a first-person in the plural, so the verb must be conjugated in this form. Nosotros tenemos.
Tamara and I are hungry and thirsty.