"For both of them to go ..."

In the following dialog at a funeral for the parents of two children who died in an accident:

They were in an accident… For both of them to go… I heard the
other person wasn’t watching the road.

I don’t really sure about the meaning of the sentence: “For both of them to go…”

Is it talking about the cause of the accident in the previous sentence or about the sequence after “they were in an accident”?