Highlands Recommendations

Hello abimorrison
Have a look at Undiscovered Scotland's website's interactive map with many interesting places of interest to explore.
https://www.undiscoveredscotland.co.uk/

The site also includes a driving routes map, again interactive, that is an additional excellent resource.
https://www.undiscoveredscotland.co.uk/ustours/index.html We did a couple of these routes and enjoyed each. The Gairloch Poolewe route takes in the Corrieshalloch Gorge. It has a bouncy, swaying suspension bridge over the gorge that your 14yos might find an interesting experience .. if they are not afraid of heights.

If you head to the west side of Scotland you are apt to encounter midgies so you'll need to be prepared with insect repellant. Smidge is a popular brand and the company has a midge forecast map that I believe begins updates in May.
https://www.smidgeup.com/midge-forecast/

Happy planning!

Your kids might enjoy the ferry from Ullapool (about an hour drive from Inverness) to Stornaway (Isle of Lewis). You could easily drive down to the stones of Callanish and various other sites such as mentioned here - Visit Scotland Lewis & Harris. You could stay one or two nights in Stornaway before catching the ferry back to Ullapool. Your kids might enjoy spotting dolphins and maybe whales from the ferry. Calmac is the ferry company website.

You probably won't encounter midges on Lewis. It's generally quite breezy and midges don't like wind! The midge forecast is just a marketing tool by Smidge! The product is good and available in most supermarkets in the Highlands as well as outdoor shops. Midges like damp, shady conditions. Dusk is prime time for them! Don't let the fear of midges put you off. You won't see any in Inverness!

Thankfully midge hoods £5 ish are widely available and worth £500 for your sanities sake .
Big on Skye girls recommendation.
The outer isles are much quieter than the usual " must dos " in the Great Glen area
Uig Sands is not far from Callanish ,great little museum and cafe there, featuring the Chessmen.
For something extraordinary, check the Lindanorgrovefoundation.

Your kids might enjoy the ferry from Ullapool (about an hour drive from Inverness) to Stornoway (Isle of Lewis).

I agree with Jacqui. The Stornoway - Ullapool ferry is large with multiple lounges, a TV area, cafe, bar, game area, and outside seating where you can look for dolphins, whales and other marine life. It's a really nice and very fun ferry ride, and I think any age kid would love it.

And I loved Lewis! I stayed right outside Stornoway (a lovely small city on the sea) and would love to go back. So many cool sights, including the Calanais standing stones, the Blackhouse Village, gorgeous beaches, and Lews Castle. Most of them are contained within the same area so they're not really spread out. It's definitely easier to get to them. And big plus is that it's not nearly as crowded as Skye will be in August. Most of the tourists there are from the UK or other parts of Europe. It's really a lovely place and I want to go back one day.

Thanks to all!

I'm going to add a strong recommendation to consider visiting Dunottar Castle near Stonehaven, south of Aberdeen. It's spectacular, both the castle itself and the views of the sea from the property.