if they are really set for going those dates, i would recommend offsite. for the price you would pay for onsite, you can get an entire condo or townhouse offsite. again, not ideal for a firstimer who wants to experinece all of the "surrounded by magic" feel of staying onsite at WDW....but a great experinece all the same. it is especially ideal if they were going to need two rooms anyway. many condos are at least 2 bedrooms, some 3 and the town houses are generally 3 bedrooms (with 3 baths and some even have a priviate pool.)
we have done onsite for years and tried offsite at a townhouse this past summer. loved it. so many pluses. will i ever stay onsite again...sure i will, but i certainly won't give a 2nd thought to booking offsite if the situation ($, availabilty onsite, need for more than one room or extra space, etc.) called for it.