The seaplane at Prestwick was almost certainly G-SEAI, now based on Loch Lomond. It was based there for a while.
The C5s were all there together. Carrying out logistics flights during some conflict or other. Bosnia maybe.
The Prestwick images are all around 6 or more years old. The evidence being the non existence of the Polar Air Cargo hangar which was constructed in 2000.
The other runways were the remains of RAF Ayr (Heathfield), also known as HMS Wagtail for a period during it's life.
More info here:
RAF Ayr/Heathfield