Looking for recommendations for half day fly fishing in the Jackson Hole/Teton Village/GTNP area in late July. Group of 3, including my 12 year old son, 70 year old dad, and 40 year old husband. 12 yo and 70 yo have never fly fished before. Any recommendations as far as going through the GTNP park or booking through a fly fishing school in Jackson - there are lots of options, they all look the same! I'm guessing that paying a guide rather than trying on your own is the way to do it, but looking for advice.

Fly fishing is not easy. I would take lessons before hiring a guide out west.
Orvis offers excellent fly fishing workshops throughout the US -
https://www.orvis.com/fly-fishing-schools
And then hire a guide when you are out there.
Snake River Angler -
Fly Fishing Trips - Jackson Hole & Grand Teton Fly Fishing Guided Trips
Be sure to tip your guide!

Starrs is correct that fly fishing IS not exactly easy and if you can get some lessons before it is good. However a guide WILL give lessons as you fish there.

My husband is a fanatical fly fisherman.

I don't know how much time a half day lesson is, but it might take the newbies an hour or more to understand the gear and (hopefully) get the hang of casting. (For me, it has never really "clicked.") On my husband's first day of fly fishing 25 years ago, he fished for 6 straight hours because he was having a blast. He had experience with ocean fishing but had never tried fly fishing. His first guide had to teach him from step 1.

There are how-to videos on YouTube to understand the "science" of casting.

As you see the difference between a half day and whole day is really small.. Fly fishing is a magical time to spend outdoors.

starrs is spot on. I would ask the knowledge people at Snake River Angle about your plans and what they would recommend. They are great!