I used to live in Dumfries, moved away quite a few years ago so my knowledge of the area isn't up to date but if you are looking for pottery/ceramics specifically I have some nice pieces from Barnbarroch Pottery which is near Dalbeattie. Which would fit in fairly well with a trip to the Kirkcudbright/Castle Douglas area. I can see recent posts from the pottery on social media so they are still there after all these years.
There's also the Gracefield Arts Centre in Dumfries which holds exhibitions of local work.
Dumfries and Galloway doesn't have lots of fast major roads and the public transport network wasn't great when I lived there so there is a lot of driving involved and it can feel like it takes a while to get to places. But the countryside and the smaller towns and villages are lovely.
If your teens like outdoorsy things there is a lot of that in D&G, the forests (Ae, Mabie) have walking and biking tracks and there is a big mountain biking trails network in D&G (the 7 Stanes network). I used to do a lot of walking, there are some nice hillwalks in the area - Criffel and Screel spring to mind as walks to look at if you can fit in a day walking. There is also a water sports activity centre at Loch Ken.
Apart from the Gracefield Arts Centre and the Forest of Ae, all of these are a fair way from Amisfield but if you don't mind the driving you should still be able to see plenty further west in the region.
When I lived in the area, the Thornhill and Moniaive areas were well known for crafts and artists so it might be worth looking for potters etc around there as it would be not too far from Amisfield. Or Moffat, which is a direct drive further north from Amisfield, it always seemed to have lots of craft places and cafes, and there are some lovely walks around Moffat - the Grey Mare's Tail waterfall walk was a favourite