Possibly the best thing is to bring a buddy. I see that this is a family trip. We’ve had late teens/early twenties with us on family trips.
Well before the trip I would ask the teen/20s person what they remembered. What they liked. Didn’t like. These can be informative but the single best thing is bringing a buddy.
One 20 year old had an 18 yo robotics club friend with us. The 18 yo’s parents paid for food and admissions tickets at Disney as well as transportation. I think they were happy for their kid to “go back to Disney” and they didn’t have to. 
Those two were out the door before 7 every morning, rope dropping a park. DH and I moved slower. 
We often met up mid day back at our resort as we took breaks from people, noise and heat.
The only stipulation I had was that we meet for supper. They always did and we had some great conversations about their day.
Regarding photos, I’ve always liked moseying around here and there. One of my favorites over the years is the stack of trunks off to the side waiting further transport at Jungle Cruise I think it was. Another place like that is Expedition Everest. The whole AK is awash with nifty shots here and there.
As is Epcot.
Tho back when I was using 35mm slide film I could expose a 36 exp roll in an hour just anywhere. I often heard from a family member “Why are you taking a picture of that?”
Maybe pick a two or three must do things at each park and then let him and his camera wander. Agreeing to meet at a meal time.
The DME app makes keeping on schedule easy. Never had to tell the 20 yr old anything - he could look it up.
We had a 17 yo with us one trip. He wanted more sleep than food, so he’d join us about 9 am at the park of the morning. For this trip we had tacked on 2 nights at a resort we’d stayed at 20 yrs prior. Since we’d already done 7 nights, the extra two were for extras, repeats, shopping and as it turned out, the resort arcade. The 17 yo thoroughly enjoyed a couple of the games - not available around here. Spent the whole weekend - other than suppers with the family - at the arcade, memorably.
That same person is now 35. His last trip was when he was 28, with his 3 daughters. And the rest of the extended family. 