My advice would be to sit down and get detail on what accountabilities and expectations go along with this "mother's helper". It sounds like it's a maiden run for both you and the family, and all types of confusion and misunderstandings can come up. WDW isn't always a magical place when things go bad, as the countless threads on that subject prove. Once you know what's expected and what you can provide, both sides can make informed decisions. WDW is expensive, so if you are going to pay for any part of the vacation, make sure you know the costs.