The question is: ¿Qué nos aconsejas que hagamos? which means "What do you advise us to do?" The options are listed below.
a. Les aconsejo que vengan al parque. - "I advise you to come to the park."
b. Les aconsejo que vayan al parque. - "I advise you to go to the park."
c. Les aconsejaremos que vayan al parque. - "We will advise them to go to the park."
Option C is not right, as it is in future tense, and refers to someone other than the original speaker ("them"). That leaves the first two options. Either of them would make sense, however since there is no context for this sentence, I'm inclined to say option B is correct, as A implies the answerer is already at the park.
The most correct answer is option B - Les aconsejo que vayan al parque.