Tell your family that flying in/out of CUN is a relative breeze and they shouldn't be worried at all. Customs is fairly efficient and in general, I've found the agents to be even more friendly than some of the surly ones you are bound to run into in the U.S. (especially in Atlanta).

The only recommendation I would make is to reserve your ground transportation prior to arriving in CUN as the tour sales people will drive you nuts exiting baggage claim. Full of barkers, it's like walking the midway of a county fair on a slow day.

Tell you family to have a fantastic time!