I agree, I think it's not said. The issues mentioned in Dead of Night could have happened during weekend stayovers or when the grandmother visited while the parents were at work or something.
However, I believe, had their parents lived, we would have seen them in the hospital when Richard was shot. However, there's just Sarah and Amy.
However, I've stumbled over several fics that include the parents.

Edit: I need to find another word for however. LOL