One thing to note - if you get one Preferred annual pass, you get 10% off almost all food and merchandise during your stay. With that length of stay and a family of four, it might totally be worth it.
I've never used EP. I know that some people rave about it, but IMHO with lower park crowds and a 5 full day stay, it may not be totally necessary. Using early entry and the single rider lanes (which they have on almost all of the big rides), you can get A LOT done without sacrificing much. But your mileage may vary - it depends on how flexible you feel that your family can be.