What I never understood about these two is why not simply change the date the two marries? They all end up dying due to the newly wed couple driving off in such bad weather, they should push for the two to be married before that date or after to avoid the bad weather causes their tragedy. Their knowledge of the future would allow them to invest in stocks or if they are knowledgable about sports double their bank quickly, with vast money and Da's sisters diary they should be able to circumvent this fate easily (like offer to pay for the honeymoon and arrange it such to avoid that particular drive, on that particular night, and most of all that particular weather).