From strictly a ticket stand point 10 day, no hopping, no expiration tickets will be less expensive than an AP by about $30 a piece. If they do elect to stay off property the AP's will pull ahead by $80 due to free parking. However, you only need 1 AP to get free parking so the best option would be for 1 AP and 1 10 day no hopping, no expiration ticket.
For the 2 sets of grand kids they really have no choice but to buy separate 5 day base tickets for each group.
TiWL will only be a value to them if they plan on eating at fair number of TS restaurants. If they plan on breakfast and dinner out of the parks and hitting a QS place for lunch then the savings will be minimal if at all. If they plan on hitting places like Ohana, CRT, Chef Mickey, etc on each trip then TiWL will pay off. The only way to know for sure is to run the numbers. There is also a mandatory 18% gratuity when using the TiWL. This is no big deal if they typically tip 15%-20% but if they are they typically do not tip at that rate the savings will begin to erode.
You also might want to inquire as to why they are staying off property. Many times you will find that when you add in rental cars, time, parking, et,c off property is equal to or more expensive than on property. But yet again every situation is a little different and you will need to run the numbers for their particular situation.