A coastal and an olive are not good things to keep together. Your snakes don't "want" to be together. Snakes are solitary animals. Forcing them to live together will cause a fair amount of stress for them both. Stress means decreased immune system, meaning your snakes could get sick and die.
Think about it;
Pros: Less enclosures to take up space.
Cons: Stress, difficultly in keeping records (as it's hard to tell who did what crap, etc.), the snakes fighting, possible injuries, decreased immune system and possible death of one or BOTH of your beloved snakes.
Certainly not worth it in my opinion :|