Wow...you weren't kidding when you said short notice!! If you didn't find any discount codes on Mousesaver, then there probably aren't any available. So you probably are stuck there. Since they are driving and have a car, it may be a better deal at this late date to stay offsite and drive to the parks, versus staying onsite and using WDW transportation.... but run the numbers (quickly!) to be sure.
As far as passes, you said to "Disney, MGM and Animal Kingdom".... so I assume you mean the Magic Kingdom (MK), MGM, and AK. Your best bet for them at this time is the Park Hopper tickets, available in 4, 5, 6, and 7 day. I would imagine that the 4 day would be sufficient for them.They are available at the parks and at any local
Disney Store (no time to shop around for a discount at this point).... they could get the one day/one park passes at the parks if they don't plan on park hopping at all... might be a good idea if they are only doing the parks one - three days. Although if they buy Park Hoppers even with extra days, they never expire.
DO they realize that the World will be VERY CROWDED during this time, especially over the 4th?? Just be sure that they know this in advance. No reason to cancel or anything, just be prepared. In fact, if they plan on being at the MK on the 4th, I would suggest getting there 1 hour before park opening and staying for the day (if they are offsite). Otherwise there is a chance that the park will close due to capacity crowd and the only ones allowed in at that point are onsite guests.
For SeaWorld tickets, you can get a 10% discount if you buy and print your own e-tickets on line. Again, probably the only discount available at this late date. Hope this helps.... sorry I can't talk more.... gotta run..............P BTW.... welcome to the DIS!