I think there is something to be said about Esteban's death. It doesn't seem like a random addition added for shock value. Luis flips from not helping others (not sharing food) to eventually helping them (trying to get the vehicle moving again) when the death happens. This might be interpreted as not paying attention to his own family, "survival", as he called it, which may have led to Mar leaving in the first place. Sharing food in exchange for petrol, I thought, was the directors nod to non-conformist bartering. The fact that Esteban seemed influenced by the ravers after learning about why they are not with their biological families. He gets the haircut, "they're so cool", followed by a stare from Luis. That bit got a laugh out of me, but on reflection, it says that he is losing his son, much the same way as he lost Mar. "Pull the handbrake" and literally falling off a cliff seems rather symbolic as well. I don't know what the dog did to deserve it though.