A GAC is actually for an individual, so if each of you have different "needs" then you would each get your own GAC - especially necessarily if you might split up at all. Now, that said, if you do each have different needs then you may have to split depending on how each need can be accommodated. Check out the FAQ sticky at the top of this forum for more information.
To deal with sensory issues - you may want to use a stroller-as-wheelchair to provide an escape or "safe haven" into which the child may retreat from all the stimulation. Also, noise-reducing or noise-canceling headphones are helpful to many. Using a good touring plan to know which parks and sections of each park will be less crowded can be the most helpful, along with using Fastpasses to avoid waits. Early August is still a crowded - and very hot - time of year so planning accordingly will be your best solution. We stay hydrated and stick as close to a regular daily schedule as possible (wake up time, meals, bedtime, etc.). And kids that age enjoy downtime at the resort pools as much as the parks.
Enjoy your vacation!
