Responses
The parents probably died for months over there. As the aunt say: "They never replied to my calls for months". So something must have happened. The mother did say that crime rates are higher over there.
Since it was raining the son thought to have seen his parents, but they aren't. Only to get hit by a car.
The ghost parents seems to be looking for him for long time, and now they finally meet again. (That's the parents lingering regret so they couldn't move on until getting back to their son, thinking he was still alive. That's the reason why the parents ask someone with spiritual powers to help them find their son)
That's what I think happened
after they saw him die maybe they quit their job and mourned then one day they died in an accident or maybe when they saw him die they tried to approach him in a hurry but another truck was coming on the other side idk