Thank you for all your replies.
What we want are flights for our son, his partner and their infant daughter. So really, Edinburgh is their nearest airport, so that would be best, however, what I wasn't prepared for was the hike in prices, as compared even to Glasgow or Newcastle. We will keep looking, and may wait a bit longer, just to see if prices change.
Skyscanner puts first choice as cheapest, and what they really need is direct flights.
We will see how it all works out.
Also, it seems that September is quite expensive, and yet, I thought it would be a bit cheaper after school hols were over.