There are lots of restaurants inside hotels that are character meals.
Grand Floridian has 1900 Park Fare for Cinderella and her family
Contemporary has Chef Mickey’s for Mickey and the gang
Polynesian has Ohana for Lilo, Stitch, Mickey, and Pluto
Beach/Yacht Club has Cape May Cafe for Mickey and the Crew; short walk to Boardwalk for breakfast at Tratorra al Forna for Ariel, Prince Eric, Rapunzel and Flynn
I don’t know of any specific meet and greets at the hotels besides restaurants with character meals, but someone else may.
If they’re obsessed with characters, any of the deluxe hotels I mentioned are all great locations and close to parks where there are lots of meet and greets. If those hotels are out of your price range, you can still eat at those restaurants and get easily to the parks while staying at a value or moderate hotel.
Here’s a tip: Check out Kenny The Pirate’s character locator site for lots of info on meet and greets.
Have a great trip! You’re all going to love it!