That is the peak season for Disney. I doubt very much you'll get any kind of discount with Disney. you might be able to find deals outside of Disney, but we learned the hard way, not to fall for it. Your far better reccommending a value resort with Disney than even a 5star DTD resort. If someone wants to stay off site, dont give them grief, but dont reccommend it to anyone wither.
Your guests should really be booking already, so I would reccommend you have them decide where they want to stay and possibly pair them with other travelers who might want to split a room. Have them look at the home away from home resorts as well because you can get up to 12 people in the grand villas, also good for splitting with another family and with full kitchens they can dine in and save on food.