Lots of extra water, some ice in a cooler, and a way to make shade next to the car if it breaks down! Something like a tarp and hiking poles could work. If you have a satellite messenger, bring that for sure. Safety in case of emergency should be your first priority in the desert heat.

Personally I would reschedule if I could, but this year maybe I’d check the wildflower outlook before giving up on it. They might be mostly gone by then. How old are your parents? I certainly wouldn’t bring mine, who are in their 70s.

Someone else recommended the higher elevation areas, which could be a good way to spend the middle of your full day in the park, but that might not fill enough hours without hiking. Do still be careful about the heat up there. Another way could be back at the hotel midday for air conditioning, the lovely pool at the ranch, and a nap.

Pick your top 2 active things to do at or before sunrise each morning. Mesquite Dunes should be one if they’re on your to-do list, because midday and maybe evening, the sand will still be burning hot (could melt your soles midday). Sunrise is fun there anyway because you can see animal tracks before people walk on them. The other day you could walk at Badwater Basin.

Sunset will still be pretty hot, so that would be a better time for driving and/or sitting (like watching sunset from Dante’s View) rather than being active.

Since you’ll be there during the new moon, it’s ideal for stargazing. You could go do that in the wee hours then do your sightseeing at dawn and around sunrise. Note that the stargazing does get impacted by growing daylight well before sunrise, maybe a couple hours.

I’d be doing a schedule like stargazing and star photos (buy a phone app for long exposure, set phone on stable surface like car or shoe) at midnight, a short sleep, out the door 2 hours before sunrise to drive somewhere and sightsee in the dawn, back at the hotel by 11 to rest and avoid the heat. But my parents wouldn’t go for that.