"My uncle and my aunt were walking on that street when they saw my car."
Translation:Meu tio e minha tia estavam caminhando naquela rua quando viram meu carro.
"viram". Like in English, we have to use the Simple Past when an action in the past interrupts an action that was going on in the past. "Viam" is pretérito imperfeito, which is not used in this kind of structure.