Can you get an adapter which allows 2 people with headphones to listen to a movie?

You can get earphone splitters - not sure whether Apple sell any, but there are some on Amazon e.g. from Belkin

There is at least one set available in the Apple Store (saw them yesterday), but you can get them at any electronics store.

No joking, but I was in the DOLLAR TREE yesterday and they had a bunch of them (they were white too) 😉 Your local dollar tree may have them too.