Don't be afraid to go to City Hall or Commerce Dept in DCA if it does get to be too much for him! The crowds at DL are very different from WDW, they are much more intense and it's really a lot to process. Everything, from lines to walkways to show viewing areas is SMALL, thousands of people shoved in small areas makes it an intense experience. It's not uncommon for Adventureland to come to standstill at night after Fantasmic show #1 clears out (but DL has been trying crowd control methods of keeping traffic moving).
Day 1 is definitely doable. Day 2 is another matter. EMH is great, make sure you are there for rope drop. At rope drop everyone proceeds to race for PP, by the time you get there you may be lucky and have a 20 minute wait, you might not and you'll have the normal 30-40 minute wait. TBH, skip PP. It's not THAT different from WDW. You can do a lot during EMH if you skip PP. I'd start with Alice and Dumbo, it's a nice time to do Snow White and Pinochio with 5 minute waits. Toad will fill as people get off PP and go to the next ride so slip Toad in there after Alice and Dumbo. Canal boats next and then time for a Tea Party! (Fit in your MPs as they come up) The walk through of the castle can literally be done whenever the area is not blocked off for fireworks, never a wait. You will all be very tired after this, Plaza Inn out here does a great QS lunch, their fried chicken is legendary. Blue Bayou if that's on your bucket list for TS. Carnation Cafe is the most classic restaurant, comfort food all the way, TS. Monte Cristo is great for splitting and can found at Cafe Orleans, TS. Plaza Inn and Carnation Cafe have split inside/outside seating, Blue Bayou all inside, Cafe Orleans 75% outside. Inside = air conditioning!!!! And you're going in August, 100 degree days are definitely possible. You can request inside seating at Carnation and have a good shot at getting it. Cafe Orleans is tough because there just isn't much. Winnie after lunch? Grab anything you miss when you come back that night (do realize part of Fantasyland will be closed during fireworks, and canal boats are much better in the day if you only do them once). Pick up MPs for the afternoon and evening for some of those bigger attractions you might want to repeat like BTMRR, Indy.
Everything on Main St is 100% skip able so skip it, you won't have time. Do catch the train for a round-the-Kingdom trip! Our train is much more convenient out here than at WDW.
Where are you staying? On-site, 2pm to 4pm will be fine for a break but I don't think you are since you mention only have MM. Off-site but walking to the park 2pm-5pm to account for the longer security lines. Off-site but driving to the park 2pm-5:30pm because traffic.
Wed is doable.
Remember, upgrading to a park hopper will cost the same if you do it on the first day of the trip or the last. Also, you can book MPs for either park so pick up MPs for GOTG, IncrediCoaster for sure. Soarin is the same as WDW. Grizzly has the potential to soak you fyi.
Fri at DtD. Is this departure day? DtD DLR sucks right now fyi. World of Disney is half under construction, Rainforest cafe/espn zone/movie theater will be in the process of being torn down. There wasn't much to keep one's interest besides browsing shops for a couple hours before this and now- there's even less. I'd REALLY consider upgrading to a 5 day ticket. If you have to chose park hopper upgrade for a 4 day ticket or 5 day non-park hopper ticket I'd do the 5 day non-park hopper. Even if you do Day 5 without MP.
Phew! much planning!