"What do your parents think?"
Translation:¿Qué piensan tus padres?
Shouldn't it be 'Que piensan a tus padres? '
I'm still very confused about when to use 'a' when referring to people or animals...
Here, "parents" is the subject of the sentence, doing the thinking.
The "personal a" is used when the person or pet/animal is the direct object of the sentence.
Although direct objects often come at the end of the sentence, sometimes the subject comes there. So location is not always a sure sign that a "personal a" is needed.
It sounds very odd to mention a subject after an interrogative «qué», «cómo» or «dónde» (but it's okay after a «por qué»).
Duo gave me the solution 'Qué cosa piensan tus padres?' which I'm pretty sure isn't right.