If you go to the Black Isle early ish in the morning you should see dolphins, we have managed to see them every time we visit 
The fairy pools on the Isle of Skye are amazing but it might be a bit to far.
Aviemore is well worth a visit and only an hour away from Inverness, drive up then hop on the train to the top, the view is unbelievable! There are lots of parks and a fair few shops too, they also have a great go ape type thing for the older ones. You can also do a walk with the reindeer.
How many full days do you have?
Isle of Skye would be a very long full day to make the most of it, I would choose Aviemore over the Isle of Skye purely as you won't have enough time to do it justice.
The Black Isle would only need to be an hour or so in the morning (take a flask for a hot drink 😉), you could then wander around Inverness for the day and visit the swimming pool.
Fort George is so stunning but is quite a drive, the bridge is pretty cool. It's the very end of Loch Ness.
Loch Ness itself doesn't do it for me, but the children might like the Nessy stories, castle Urquart is expensive and can get busy.
The pics below are Fort George!
Either way you will have a fab time