Of the hotels you are looking at, I'd say maybe give AKL a try. The rates are not as expensive as the other deluxes, and seeing those animals on the Savannah is pretty magical, especially since it sounds like your grandchildren may be quite young. I would also suggest maybe consider looking at Wilderness Lodge, which has the advantage of a quick boat ride to Magic Kingdom, and a great pool and beautiful ambiance, at a much lower price point than the monorail resorts.
Promotional rates will not show up for 2019 until much closer (around 3-6 months out), so what you are looking at on the disney website is the rack rate. For a deluxe in July, I would assume an eventual discount off the rack rate of around 15-20%. That said, with price inflation, and the new star wars land, I do think it will be getting more expensive to stay deluxe. I think $500 a night is an appropriate amount to budget for somewhere like AKL or BC, especially if you get a discounts,but I would budget around $700 for GF.