It's already been said, but I have three cardinal rules of touring:
1) Open the parks. You will get more done in the first two hours than in the rest of the day. (If they really HATE getting up early, though, don't let doing that ruin your vacation.)
2) Use the FastPass system. This is where you as a Disney vet can help them most. EXPLAIN to them exactly how it works, and especially explain how you get the pass and come back later...yes it is backtracking, but it beats standing in a two hour line.
3) Have a plan...even if it's a very basic one...(We will start at Splash and BTMRR, then to adventureland, then fantasyland.) Give them a hand to decide which parks on which days. (If they are staying off-site...help them avoid extra-magic hour days.)
If they want lots of info, have them pick up the Unofficial Guide, my favorite guide book, and have it handy as a reference.
Try to make them understand how hot and crowded it will be, and how if they start to burn out take a break.
Finally, if they don't want to listen to what you have to say, don't feel bad...most people don't really believe what it's like there.
SkierPete